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2024
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Experimental Observation of Motion of Ions in a Resonantly Driven Plasma Wakefield Accelerator
M. Turner, E. Walter, C. Amoedo, N. Torrado, N. Lopes, A. Sublet, M. Bergamaschi, J. Pucek, J. Mezger, N. van Gils, L. Verra, G. Zevi Della Porta, J. Farmer, A. Clairembaud, F. Pannell, E. Gschwendtner, P. Muggli, the AWAKE Collaboration
M. Turner et al., submitted (2024), arXiv:2406.16361 [physics.plasm-ph]
Abstract:
We observe for the first time an effect on the driver caused by the motion of ions in a plasma wakefield accelerator. The effect manifests itself as a beam tail, which only occurs when sufficient motion of ions suppresses wakefields. By changing the plasma ions (helium, argon, xenon) in the experiment, we show that the effect depends inversely on the ion mass, as predicted from theory and simulations. Wakefields are driven resonantly by multiple bunches, and simulation results indicate that the ponderomotive force causes the motion of ions. In this case, the effect is also expected to depend on the amplitude of the wakefields, as also observed by varying the bunch charge. | |
2024
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Beam physics studies for a high charge and high beam quality laser-plasma accelerator
S. Marini, D. F. G. Minenna, F. Massimo, L. Batista, V. Bencini, A. Chancé, N. Chauvin, S. Doebert, J. Farmer, E. Gschwendtner, I. Moulanier, P. Muggli, D. Uriot, B. Cros, and P. A. Phi Nghiem
S. Marini et al., accepted for publication in Phys. Rev. Accelerators and Beams (2024), arXiv:2312.13883 [physics.plasm-ph]
Abstract:
Electron acceleration by laser-plasma techniques is approaching maturity and is getting ready for the construction of particle accelerators with dedicated applications. We present a general methodology showing how beam physics studies can be used to achieve a specific parameter set in a laser-plasma accelerator. Laser systems, plasma targets and magnetic components properties are designed to optimize the electron beam so as to achieve the required performances. Beam physics in its full 6D phase space is studied from electron injection to beam delivery to the end user, through plasma acceleration stage and transport line. As each beam parameter can only be modified by specific electric/magnetic field configurations, it is crucial to assign from the beginning specific roles to given accelerator sections in obtaining given beam parameters. These beam physics considerations were successfully applied to the design of a plasma based electron injector for the AWAKE Run2 experiment. Electron beam parameters were calculated using a global simulation, achieving simultaneously unprecedented high charge (100 pC) and high quality (micrometric beam emittance and size). | |
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Filamentation of a Relativistic Proton Bunch in Plasma
L. Verra, C. Amoedo, N. Torrado, A. Clairembaud, J. Mezger, F. Pannell, J. Pucek, N. van Gils, M. Bergamaschi, G. Zevi Della Porta, N. Lopes, A. Sublet, M. Turner, E. Gschwendtner, P. Muggli (AWAKE Collaboration)
L. Verra et al., AWAKE Collaboration, Phys. Rev. E 109, 055203 (2024), arXiv:2312.13883 [physics.plasm-ph]
Abstract:
We show in experiments that a long, underdense, relativistic proton bunch propagating in plasma undergoes the oblique instability, that we observe as filamentation. We determine a threshold value for the ratio between the bunch transverse size and plasma skin depth for the instability to occur. At the threshold, the outcome of the experiment alternates between filamentation and self-modulation instability (evidenced by longitudinal modulation into microbunches). Time-resolved images of the bunch density distribution reveal that filamentation grows to an observable level late along the bunch, confirming the spatio-temporal nature of the instability. We calculate the amplitude of the magnetic field generated in the plasma by the instability and show that the associated magnetic energy increases with plasma density. | |
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Hosing of a long relativistic particle bunch in plasma
T. Nechaeva, L. Verra, J. Pucek, L. Ranc, M. Bergamaschi, G. Zevi Della Porta, and P. Muggli (AWAKE Collaboration)
T. Nechaeva et al., AWAKE Collaboration, Phys. Rev. Lett. 132, 075001 (2024), arXiv:2309.03785 [physics.plasm-ph]
Abstract:
Experimental results show that hosing of a long proton bunch in plasma can be induced by wakefields driven by a short and misaligned preceding electron bunch. Hosing develops in the plane of misalignment, self-modulation in the perpendicular plane. The two processes are reproducible. Development of hosing depends on the misalignment direction. The frequencies of hosing and self-modulation are close to the plasma electron frequency. Growth of hosing depends on the misalignment extent and on the charge of the proton bunch. The results have the main characteristics of a theoretical model. | |
2023
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Development of the Self-Modulation Instability of a Relativistic Proton Bunch in Plasma
L. Verra, S. Wyler, T. Nechaeva, J. Pucek, V. Bencini, M. Bergamaschi, L. Ranc, G. Zevi Della Porta, E. Gschwendtner, P. Muggli (AWAKE Collaboration)
L. Verra et al., AWAKE Collaboration, Physics of Plasmas 30, 083104 (2023), arXiv:2305.05478 [physics.plasm-ph]
Abstract:
Self-modulation is a beam-plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length, because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the AWAKE experiment. | |
2023
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Mitigation of the onset of hosing in the linear regime through plasma frequency detuning
Mariana Moreira, Patric Muggli, Jorge Vieira
M. Moreira et al., Phys. Rev. Lett. 130, 115001 (2023) , arXiv:2207.14763 [physics.plasm-ph]
Abstract:
The hosing instability poses a feasibility risk for plasma-based accelerator concepts. We show that the growth rate for beam hosing in the linear regime (which is relevant for concepts that use a long driver) is a function of the centroid perturbation wavelength. We demonstrate how this property can be used to damp centroid oscillations by detuning the plasma response sufficiently early in the development of the instability. We also develop a new theoretical model for the early evolution of hosing. These findings have implications for the general control of an instability's growth rate. | |
2023
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Uniform onset of the long proton bunch self-modulation seeded by an electron bunch in an overdense plasma
K. Moon, E. S. Yoon, M. Chung, P. Muggli, M. Moreira, and M. A. Baistrukov
K. Moon et al., Phys. Rev. Accel. Beams 26, 111301
Abstract:
The phase, growth rate, and onset of long proton bunch self-modulation in plasma can be controlled by a preceding short charged particle bunch. In this paper, by analyzing the growth rates of the self-modulation obtained from particle-in-cell simulation results, we identify two modes of self-modulation, namely noise-seeded and externally seeded self-modulations, and investigate their onset timings. We find that a uniform onset of the self-modulation at each slice of the long proton bunch is crucial for fine-tuning its phase and amplitude. We then demonstrate that a low-energy and low-current electron seed bunch in overdense plasma generates near-axis radial wakefields similar to those observed in the blowout regime. Consequently, the resultant self-modulation is excited as a single mode simultaneously along the entire long proton bunch.Í | |
2022
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Controlled Growth of the Self-Modulation of a Relativistic Proton Bunch in Plasma
L. Verra, G. Zevi Della Porta, J. Pucek, T. Nechaeva, S. Wyler, M. Bergamaschi, E. Senes, E. Guran, J.T. Moody, M.A. Kedves, E. Gschwendtner, and P. Muggli (AWAKE Collaboration)
L. Verra et al., AWAKE Collaboration, Phys. Rev. Lett. 129, 024802 (2022), arXiv.2203.13752 [physics.acc-ph]
Abstract:
A long, narrow, relativistic charged particle bunch propagating in plasma is subject to the self-modulation (SM) instability. We show that SM of a proton bunch can be seeded by the wakefields driven by a preceding electron bunch. SM timing reproducibility and control are at the level of a small fraction of the modulation period. With this seeding method, we independently control the amplitude of the seed wakefields with the charge of the electron bunch and the growth rate of SM with the charge of the proton bunch. Seeding leads to larger growth of the wakefields than in the instability case. | |
2022
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Contribution Snowmass 2022, White Paper: AWAKE, Plasma Wakefield Acceleration of Electron Bunches for Near and Long Term Particle Physics Applications
P. Muggli, AWAKE Collaboration
P.Muggli, AWAKE Collaboration, arXiv:2203.09198 [physics.acc-ph]
Abstract:
Plasma-based accelerators have made remarkable progress over the last two decades. Their unique characteristics make them tools that can revolutionize fields of science and applications. AWAKE takes advantage of the availability of high-energy, relativistic proton bunches to drive large amplitude wakefields (∼GV/m) in a single plasma over distances sufficient to produce hundreds of GeV to TeV electron bunches. |
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2022
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European Strategy for Particle Physics - Accelerator R&D Roadmap
Editor: Nicolas MounetCERN Yellow Reports: Monographs, Vol. 1 (2022): arXiv:2201.07895 [physics.acc-ph]
Abstract:
The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to ten years, covering five topical areas identified in the Strategy update. The R&D objectives include: improvement of the performance and cost-performance of magnet and radio frequency acceleration systems; investigations of the potential of laser/plasma acceleration and energy-recovery linac techniques; and development of new concepts for muon beams and muon colliders. The goal of the roadmap is to document the collective view of the field on the next steps for the R&D programme, and to provide the evidence base to support subsequent decisions on prioritisation, resourcing and implementation. |
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2022
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European Strategy for Particle Physics - Accelerator R&D Roadmap, Chapter 4: High-gradient plasma and laser accelerators
R. Assmann, E. Gschwendtner, K. Cassou, S. Corde, L. Corner, B. Cros, M. Ferrario, S. Hooker, R. Ischebeck, A. Latina, O. Lundh, P. Muggli, P. Nghiem, J. Osterhoff, T. Raubenheimer, A. Specka, J. Vieira, M. Wing
R. Assman et al.CERN Yellow Reports: Monographs, Vol. 1 (2022): arXiv:2201.07895 [physics.acc-ph]
Abstract:
Novel high-gradient accelerators have demonstrated acceleration of electrons and positrons with electric field strengths of 1 to > 100 GeV/m. This is about 10 to 1000 times higher than achieved in RF-based accelerators, and as such they have the potential to overcome the limitations associated with RF cavities. Plasma-based accelerators have produced multi-GeV bunches with parameters approaching those suitable for a linear collider. A significant reduction in size and, perhaps, cost of future accelerators can therefore in principle be envisaged. | |
2021
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Simulation and Experimental Study of Proton Bunch Self-Modulation in Plasma with Linear Density Gradients
P.I. Morales Guzmán, P. Muggli, AWAKE Collaboration
P.I. Morales Guzmán et al., Phys. Rev. Accel. Beams 24, 101301 (2021), arXiv:2107.11369 [physics.plasm-ph]
Abstract:
We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported in arXiv:2007.14894v2: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement. |
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2021
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Long range propagation of ultrafast, ionizing laser pulses in a resonant nonlinear medium
G. Demeter, J. T. Moody, M. Aladi, A.-M. Bachmann, F. Batsch, F. Braunmuller, G. P. Djotyan, V. Fedosseev, F. Friebel, S. Gessner, E. Granados, E. Guran, M. Huther, M. A. Kedves, M. Martyanov, P. Muggli, E. Oz, H. Panuganti, B. Raczkevi, L. Verra, G. Zevi Della Porta
G. Demeter et al., Phys. Rev. A 104, 033506 (2021), arXiv:2103.14530 [physics.optics]
Abstract:
We study the propagation of 0.05-1TW power, ultrafast laser pulses in a 10 meter long rubidium vapor cell. The central wavelength of the laser is resonant with the D2 line of rubidium and the peak intensity in the 1012−1014 W/cm2 range, enough to create a plasma channel with single electron ionization. We observe the absorption of the laser pulse for low energy, a regime of transverse confinement of the laser beam by the strong resonant nonlinearity for higher energies and the transverse broadening of the output beam when the nonlinearity is saturated due to full medium ionization. We compare experimental observations of transmitted pulse energy and transverse fluence profile with the results of computer simulations modeling pulse propagation. We find a qualitative agreement between theory and experiment that corroborates the validity of our propagation model. While the quantitative differences are substantial, the results show that the model can be used to interpret the observed phenomena in terms of self-focusing and channeling of the laser pulses by the saturable nonlinearity and the transparency of the fully ionized medium along the propagation axis. |
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2021
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Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasma
F. Batsch, P. Muggli, AWAKE Collaboration
F. Batsch et al., Phys. Rev. Lett. 126, 164802 (2021), arXiv:2012.09676 [physics.plasm-ph]
Abstract:
We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufficient initial amplitude (≥(4.1±0.4) MV/m), the phase of the modulation along the bunch is reproducible from event to event, with 3 to 7% (of 2π) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated. |
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2021
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2020 roadmap on plasma accelerators
Félicie Albert, M E Couprie, Alexander Debus, Mike C Downer, Jérôme Faure, Alessandro Flacco, Leonida A Gizzi, Thomas Grismayer, Axel Huebl, Chan Joshi, M Labat, Wim P Leemans, Andreas R Maier, Stuart P D Mangles, Paul Mason, François Mathieu, Patric Muggli, Mamiko Nishiuchi, Jens Osterhoff, P P Rajeev, Ulrich Schramm, Jörg Schreiber, Alec G R Thomas, Jean-Luc Vay, Marija Vranic and Karl Zeil
F. Albert et al., 2021 New J. Phys. 23, 031101 (2021)
Abstract:
Plasma-based accelerators use the strong electromagnetic fields that can be supported by plasmas to accelerate charged particles to high energies. Accelerating field structures in plasma can be generated by powerful laser pulses or charged particle beams. This research field has recently transitioned from involving a few small-scale efforts to the development of national and international networks of scientists supported by substantial investment in large-scale research infrastructure. In this New Journal of Physics 2020 Plasma Accelerator Roadmap, perspectives from experts in this field provide a summary overview of the field and insights into the research needs and developments for an international audience of scientists, including graduate students and researchers entering the field. |
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2020
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Proton Bunch Self-Modulation in Plasma with Density Gradient
F. Braunmueller, T. Nechaeva, AWAKE Collaboration
F. Braunmueller et al., Phys. Rev. Lett. 125, 264801 (2020), arXiv:2007.14894 [physics.plasm-ph]
Abstract:
We study experimentally the effect of linear plasma density gradients on the self-modulation of a 400\,GeV proton bunch. Results show that a positive/negative gradient in/decreases the number of micro-bunches and the relative charge per micro-bunch observed after 10\,m of plasma. The measured modulation frequency also in/decreases. % with in/decreasing gradient. With the largest positive gradient we observe two frequencies in the modulation power spectrum. Results are consistent with changes in wakefields' phase velocity due to plasma density gradient adding to the slow wakefields' phase velocity during self-modulation growth predicted by linear theory. |
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2020
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Seeding self-modulation of a long proton bunch with a short electron bunch
P. Muggli, P. I. Morales Guzman, A.-M. Bachmann, M. Huether, M. Moreira, M. Turner, J. Vieira
P. Muggli et al., J. Phys.: Conf. Ser. 1596 012065 (2020)
Abstract:
We briefly compare in numerical simulations the relativistic ionization front and electron bunch seeding of the self-modulation of a relativistic proton bunch in plasma. When parameters are such that initial wakefields are equal with the two seeding methods, the evolution of the maximum longitudinal wakefields along the plasma are similar. We also propose a possible seeding/injection scheme using a single plasma that we will study in upcoming simulations works. |
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2020
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Predicting the Trajectory of a Relativistic Electron Beam for External Injection in Plasma Wakefields
F. Peña Asmus, F. M. Velotti, M. Turner, S. Gessner, M. Martyanov, C. Bracco, B. Goddard and P. Muggli
F. Peña Asmus et al., J. Phys.: Conf. Ser. 1596 012048 (2020)
Abstract:
We use beam position measurements over the first part of the AWAKE electron beamline, together with beamline modeling, to deduce the beam average momentum and to predict the beam position in the second part of the beamline. Results show that using only the first five beam position monitors leads to much larger differences between predicted and measured positions at the last two monitors than when using the first eight beam position monitors. These last two positions can in principle be used with ballistic calculations to predict the parameters of closest approach of the electron bunch with the proton beam. In external injection experiments of the electron bunch into plasma wakefields driven by the proton bunch, only the first five beam position monitors measurements remain un-affected by the presence of the much higher charge proton bunch. Results with eight beam position monitors show the prediction method works in principle to determine electron and proton beams closest approach within the wakefields width (<1 mm), corresponding to injection of electrons into the wakefields. Using five beam position monitors is not sufficient. |
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2020
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Determination of the Charge per Micro-Bunch of a Self-Modulated Proton Bunch using a Streak Camera
A.-M. Bachmann, P. Muggli
A.-M. Bachmann, P. Muggli, J. Phys.: Conf. Ser. 1596 012005 (2020)
Abstract:
The Advanced Wakefield Experiment (AWAKE) develops the first plasma wakefield accelerator with a high-energy proton bunch as driver. The 400GeV bunch from CERN Super Proton Synchrotron (SPS) propagates through a 10m long rubidium plasma, ionized by a 4TW laser pulse co-propagating with the proton bunch. The relativistic ionization front seeds a self-modulation process. The seeded self-modulation transforms the bunch into a train of micro-bunches resonantly driving wakefields. We measure the density modulation of the bunch, in time, with a streak camera with picosecond resolution. The observed effect corresponds to alternating focusing and defocusing fields. We present a procedure recovering the charge of the bunch from the experimental streak camera images containing the charge density. These studies are important to determine the charge per micro-bunch along the modulated proton bunch and to understand the wakefields driven by the modulated bunch. |
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2020
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Study of external electron beam injection into proton driven plasma wakefields for AWAKE Run2
L. Verra, E. Gschwendtner, P. Muggli
L. Verra et al., J. Phys.: Conf. Ser. 1596 012007 (2020)
Abstract:
We describe an external electron injection scheme for the AWAKE experiment. We use scattering in two foils, that are necessary as vacuum window and laser beam dump, to decrease the betatron function of the incoming electron beam for injection and matching into plasma wakefields driven by a self-modulated proton bunch. We show that, for a total aluminum foil thickness of ∼280μm, multiple Coulomb scattering increases the beam emittance by a factor of ∼10 and decreases the betatron function by a factor of ∼3. The plasma in the accelerator is created by a ionizing laser pulse, counter-propagating with respect to the electron beam. This allows for the electron bunch to enter the plasma through an "infinitely" sharp vapor-plasma boundary, away from the foils. |
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2020
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Physics to plan AWAKE Run 2
P. Muggli for the AWAKE Collaboration
P. Muggli, J. Phys.: Conf. Ser. 1596 012008 (2020)
Abstract:
We briefly describe the basic physics principles considered for planning of the AWAKE Run 2 experiment. These principles are based on experimental results obtained during Run 1 and knowledge obtained from numerical simulation results and other experiments. The goal of Run 2 is to accelerate an electron bunch with a narrow relative energy spread and an emittance sufficiently low for applications. The experiment will use two plasmas, electron bunch seeding for the SM process, on-axis external injection of an electron bunch and electron bunch parameters to reach plasma blow-out, beam loading and beam matching. |
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2020
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Experimental Study of Wakefields Driven by a Self-Modulating Proton Bunch in Plasma
M. Turner, P. Muggli, et al.
M. Turner, P. Muggli, The AWAKE Collaboration, Phys. Rev. Accel. Beams 23, 081302, (2020), arXiv:2005.05277 [physics.acc-ph]
Abstract:
We study experimentally the longitudinal and transverse wakefields driven by a highly relativistic proton bunch during self-modulation in plasma. We show that the wakefields' growth and amplitude increases with increasing seed amplitude as well as with the proton bunch charge in the plasma. We study transverse wakefields using the maximum radius of the proton bunch distribution on a screen downstream from the plasma. |
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2020
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Electron beam characterization with beam loss monitors in AWAKE
L. Verra, M. Turner, S. Gessner, E. Gschwendtner, F. Velotti, P. Muggli
L. Verra et al., Phys. Rev. Accel. Beams 23, 032803 (2020), arXiv:1912.05009 [physics.acc-ph]
Abstract:
We present a method to measure transverse size and position of an electron or proton beam, close to the injection point in plasma wakefields, where other diagnostics are not available. We show that transverse size measurements are in agreement with values expected from the beam optics with a <10% uncertainty. We confirm the deflection of the low-energy 18 MeV electron beam trajectory by the Earth's magnetic field. This measurement can be used to correct for this effect and set proper electron bunch injection parameters. The AWAKE experiment relies on these measurements for optimizing electron injection. |
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2019
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Interaction of Ultra Relativistic e- e+ Fireball Beam with Plasma
Nitin Shukla, Samuel F Martins, Patric Muggli, Jorge Vieira and Luis O Silva
Nitin Shukla et al., New Journal of Physics, 22, 011330 (2019)
Abstract:
Ab initio simulations of the propagation in a plasma of a soon to be available relativistic electron-positron beam or fireball beam provide an effective mean for the study of microphysics relevant to astrophysical scenarios. We show that the current filamentation instability associated with some of these scenarios reaches saturation after only 10cm of propagation in a typical laboratory plasma with a density ~1017cm-3. The different regimes of the instability, from the purely transverse to the mixed mode filamentation, can be accessed by varying the background plasma density. The instability generates large local plasma gradients, intense transverse magnetic fields, and enhanced emission of radiation. We suggest that these effects may be observed experimentally for the first time. |
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2019
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2019
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2019
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Influence of proton bunch and plasma parameters on the AWAKE experiment
Mariana Moreira, Jorge Vieira, Patric Muggli
M. Moreira et al., Phys. Rev. Accel. Beams 22, 031301 (2019), arXiv:1811.08277
Abstract:
We use particle-in-cell (PIC) simulations to study the effects of variations of the incoming 400 GeV proton bunch parameters on the amplitude and phase of the wakefields resulting from a seeded self-modulation (SSM) process. We find that these effects are largest during the growth of the SSM, i.e. over the first five to six meters of plasma with an electron density of 7x1014 cm−3. However, for variations of any single parameter by ±5%, effects after the SSM saturation point are small. In particular, the phase variations correspond to much less than a quarter wakefield period, making deterministic injection of electrons (or positrons) into the accelerating and focusing phase of the wakefields in principle possible. We use the wakefields from the simulations and a simple test electron model to determine the injection position along the bunch and along the plasma leading to the largest energy gain. This analysis includes the dephasing of the electrons with respect to the wakefields that is expected during the growth of the SSM. We find that the optimum position along the proton bunch is at ξ≅−1.5σzb, and that the optimal range for injection along the plasma (for a highest final energy of ∼1.6 GeV after 10 m) is 5-6 m. The latter result is obtained from a PIC simulation that tests different injection points and is also used to validate the model mentioned above. |
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2019
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Experimental observation of proton bunch modulation in a plasma, at varying plasma densities
The AWAKE Collaboration
The AWAKE Collaboration, Phys. Rev. Lett. 122, 054802 (2019), arXiv:1809.04478
Abstract:
We give direct experimental evidence for the observation of the full transverse self-modulation of a relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a density modulation resulting from radial wakefield effects with a period reciprocal to the plasma frequency. We show that the modulation is seeded by using an intense laser pulse co-propagating with the proton bunch which creates a relativistic ionization front within the bunch. We show by varying the plasma density over one order of magnitude that the modulation period scales with the expected dependence on the plasma density. |
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2019
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Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch
M. Turner, the AWAKE Collaboration
M. Turner et al., Phys. Rev. Lett. 122, 054801 (2019), arXiv:1809.01191
Abstract:
We measure the effects of transverse wakefields driven by a relativistic proton bunch in plasma with densities of 2.1×1014 and 7.7×1014electrons/cm3. We show that these wakefields periodically defocus the proton bunch itself, consistently with the development of the seeded self-modulation process. We show that the defocusing increases both along the bunch and along the plasma by using time resolved and time-integrated measurements of the proton bunch transverse distribution. We evaluate the transverse wakefield amplitudes and show that they exceed their seed value (<15MV/m) and reach over 300MV/m. All these results confirm the development of the seeded self-modulation process, a necessary condition for external injection of low energy and acceleration of electrons to multi-GeV energy levels. |
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2018
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Schlieren imaging for the determination of the radius of an excited rubidium column
A.-M. Bachmann, M. Martyanov, J. Moody, A. Pukhov, P. Muggli
A.-M. Bachmann et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 387 (2018).
Abstract:
AWAKE develops a new plasma wakefield accelerator using the CERN SPS proton bunch as a driver Muggli et al. (2017). The proton bunch propagates through a 10m long rubidium plasma, induced by an ionizing laser pulse. The co-propagation of the laser pulse with the proton bunch seeds the self modulation instability of the proton bunch that transforms the bunch to a train with hundreds of bunchlets which drive the wakefields. Therefore the plasma radius must exceed the proton bunch radius. Schlieren imaging is proposed to determine the plasma radius on both ends of the vapor source. We use Schlieren imaging to estimate the radius of a column of excited rubidium atoms. A tunable, narrow bandwidth laser is split into a beam for the excitation of the rubidium vapor and for the visualization using Schlieren imaging. With a laser wavelength very close to the D2 transition line of rubidium (λ~780nm), it is possible to excite a column of rubidium atoms in a small vapor source, to record a Schlieren signal of the excitation column and to estimate its radius. We describe the method and show the results of the measurement. |
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2018
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Interferometer-based high-accuracy white light measurement of neutral rubidium density and gradient at AWAKE
F. Batsch, M. Martyanov, E. Oez, J. Moody, E.Gschwendtner, A. Caldwell, P. Muggli
F. Batsch et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 359 (2018).
Abstract:
The AWAKE experiment requires an automated online rubidium (Rb) plasma density and gradient diagnostic for densities between 1 and 10x1014 cm−3. A linear density gradient along the plasma source at the percent level may be useful to improve the electron acceleration process. Because of full laser ionization of Rb vapor to Rb+ within a radius of 1 mm, the plasma density equals the vapor density. We measure the Rb vapor densities at both ends of the source, with high precision using, white light interferometry. At either source end, broadband laser light passes a remotely controlled Mach–Zehnder interferometer built out of single mode fibers. The resulting interference signal, influenced by dispersion in the vicinity of the Rb D1 and D2 transitions, is dispersed in wavelength by a spectrograph. Fully automated Fourier-based signal conditioning and a fit algorithm yield the density with an uncertainty between the measurements at both ends of 0.11 to 0.46% over the entire density range. These densities used to operate the plasma source are displayed live in the control room. |
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2018
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Acceleration of electrons in the plasma wakefield of a proton bunch
AWAKE Collaboration
AWAKE Collaboration, Nature (London) 561, 363 (2018).
Abstract:
High-energy particle accelerators have been crucial in providing a deeper understanding of fundamental particles and the forces that govern their interactions. To increase the energy of the particles or to reduce the size of the accelerator, new acceleration schemes need to be developed. Plasma wakefield acceleration1,2,3,4,5, in which the electrons in a plasma are excited, leading to strong electric fields (so called ‚wakefields), is one such promising acceleration technique. Experiments have shown that an intense laser pulse6,7,8,9 or electron bunch10,11 traversing a plasma can drive electric fields of tens of gigavolts per metre and above‚ well beyond those achieved in conventional radio-frequency accelerators (about 0.1 gigavolt per metre). However, the low stored energy of laser pulses and electron bunches means that multiple acceleration stages are needed to reach very high particle energies5,12. The use of proton bunches is compelling because they have the potential to drive wakefields and to accelerate electrons to high energy in a single acceleration stage13. Long, thin proton bunches can be used because they undergo a process called self-modulation14,15,16, a particle‚ plasma interaction that splits the bunch longitudinally into a series of high-density microbunches, which then act resonantly to create large wakefields. The Advanced Wakefield (AWAKE) experiment at CERN17,18,19 uses high-intensity proton bunches- in which each proton has an energy of 400 gigaelectronvolts, resulting in a total bunch energy of 19 kilojoules‚ to drive a wakefield in a ten-metre-long plasma. Electron bunches are then injected into this wakefield. Here we present measurements of electrons accelerated up to two gigaelectronvolts at the AWAKE experiment, in a demonstration of proton-driven plasma wakefield acceleration. Measurements were conducted under various plasma conditions and the acceleration was found to be consistent and reliable. The potential for this scheme to produce very high-energy electron bunches in a single accelerating stage20 means that our results are an important step towards the development of future high-energy particle accelerators21,22. |
|
2018
|
Signatures of the self-modulation instability of relativistic proton bunches in the AWAKE experiment
M. Moreira, J. Vieira, P. Muggli
M. Moreira et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 343 (2018).
Abstract:
We investigate numerically the detection of the self-modulation instability in a virtual detector located downstream from the plasma in the context of AWAKE. We show that the density structures, appearing in the temporally resolving virtual detector, map the transverse beam phase space distribution at the plasma exit. As a result, the proton bunch radius that appears to grow along the bunch in the detector results from the divergence increase along the bunch, related with the spatial growth of the self-modulated wakefields. In addition, asymmetric bunch structures in the detector are a result of asymmetries of the bunch divergence, and do not necessarily reflect asymmetric beam density distributions in the plasma. |
|
2018
|
Simulation study of an LWFA-based electron injector for AWAKE Run 2
B. Williamson, G. Xia, S. Döbert, S.Karsch, P. Muggli
B. Williamson et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 126 (2018).
Abstract:
The AWAKE experiment aims to demonstrate preservation of injected electron beam quality during acceleration in proton-driven plasma waves. The short bunch duration required to correctly load the wakefield is challenging to meet with the current electron injector system, given the space available to the beamline. An LWFA readily provides short-duration electron beams with sufficient charge from a compact design, and provides a scalable option for future electron acceleration experiments at AWAKE. Simulations of a shock-front injected LWFA demonstrate a 43 TW laser system would be sufficient to produce the required charge over a range of energies beyond 100 MeV. LWFA beams typically have high peak current and large divergence on exiting their native plasmas, and optimisation of bunch parameters before injection into the proton-driven wakefields is required. Compact beam transport solutions are discussed. |
|
2018
|
A method to determine the maximum radius of defocused protons after self-modulation in AWAKE
M.Turner, E.Gschwendtner, P.Muggli
M. Turner et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 123 (2018).
Abstract:
The AWAKE experiment at CERN aims to drive GV/m plasma wakefields with a self-modulated proton drive bunch, and to use them for electron acceleration. During the self-modulation process, protons are defocused by the transverse plasma wakefields and form a halo around the focused bunch core. The two-screen setup integrated in AWAKE measures the transverse, time-integrated proton bunch distribution downstream the 10 m long plasma to detect defocused protons. By measuring the maximum radius of the defocused protons we attempt calculate properties of the self-modulation. In this article, we develop a routine to identify the maximum radius of the defocused protons, based on a standard contour method. We compare the maximum radius obtained from the contour to the logarithmic lineouts of the image to show that the determined radius identifies the edge of the distribution. |
|
2018
|
Novel diagnostic for precise measurement of the modulation frequency of Seeded Self-Modulation via Coherent Transition Radiation in AWAKE
F. Braunmueller, M. Martyanova, S. Alberti, P. Muggli
F. Braunmueller et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 76 (2018).
Abstract:
We present the set-up and test-measurements of a waveguide-integrated heterodyne diagnostic for coherent transition radiation (CTR) in the AWAKE experiment. The goal of the proof-of-principle experiment AWAKE is to accelerate a witness electron bunch in the plasma wakefield of a long proton bunch that is transformed by Seeded Self-Modulation (SSM) into a train of proton micro-bunches. The CTR pulse of the self-modulated proton bunch is expected to have a frequency in the range of 90–300 GHz and a duration of 300–700 ps. The diagnostic set-up, which is designed to precisely measure the frequency and shape of this CTR-pulse, consists of two waveguide-integrated receivers that are able to measure simultaneously. They cover a significant fraction of the available plasma frequencies: the bandwidth 90–140 GHz as well as the bandwidth 255–270 GHz or 170–260 GHz in an earlier or a latter version of the set-up, respectively. The two mixers convert the CTR into a signal in the range of 5–20 GHz that is measured on a fast oscilloscope, with a high spectral resolution of 1–3 GHz dominated by the pulse length. In this contribution, we describe the measurement principle, the experimental set-up and a benchmarking of the diagnostic in AWAKE. |
|
2018
|
Seeding of the self-modulation in a long proton bunch by charge cancellation with a short electron bunch
M. Huether and P. Muggli
M. Huether et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 67 (2018).
Abstract:
In plasma wakefield accelerators (e.g. AWAKE) the proton bunch self-modulation is seeded by the ionization front of a high-power laser pulse ionizing a vapour and by the resulting steep edge of the driving bunch profile inside the created plasma. In this paper, we present calculations in 2D linear theory for a concept of a different self-modulation seeding mechanism based on electron injection. The whole proton bunch propagates through a preformed plasma and the effective beam current is modulated by the external injection of a short electron bunch at the centre of the proton beam. The resulting sharp edge in the effective beam current in the trailing part of the proton bunch is driving large wakefields that can lead to a growth of the seeded self-modulation (SSM). Furthermore, we discuss the feasibility for applications in AWAKE Run 2. |
|
2018
|
Summary of Working Group 8: Advanced and Novel Accelerators for High Energy Physics
B. Cros, P. Muggli, C.B. Schroeder, C. Tang
B. Cros et al., Nucl. Instr. and Meth. in Phys. Res. A, 909, 460 (2018).
Abstract:
We briefly summarize the work and discussions that occurred during the Working Group 8 sessions of the EAAC 2017, dedicated to advanced and novel accelerators for high energy physics applications. |
|
2018
|
Conditions for the onset of the current filamentation instability in the laboratory
N. Shukla, J. Vieira, P. Muggli, G. Sarri, R. Fonseca and L. O. Silva
N. Shukla et al., J. Plasma Phys. 84(3) 905840302 (2018).
Abstract:
The current filamentation instability (CFI) is capable of generating strong magnetic fields relevant to the explanation of radiation processes in astrophysical objects and leads to the onset of particle acceleration in collisionless shocks. Probing such extreme scenarios in the laboratory is still an open challenge. In this work, we investigate the possibility of using neutral e-/e+ beams to explore the CFI with realistic parameters, by performing two-dimensional particle-in-cell simulations. We show that CFI can occur unless the rate at which the beam expands due to finite beam emittance is larger than the CFI growth rate and as long as the role of the competing electrostatic two-stream instability (TSI) is negligible. We also show that the longitudinal energy spread, typical of plasma-based accelerated electron–positron fireball beams, plays a minor role in the growth of CFI in these scenarios. |
|
2018
|
Emittance preservation of an electron beam in a loaded quasi-linear plasma wakefield
Veronica K. Berglyd Olsen, Erik Adli, Patric Muggli
V. K. Berglyd Olsen et al., Phys. Rev. Accel. Beams 21, 011301 (2018), arXiv:1710.04858.
Abstract:
We investigate beam loading and emittance preservation for a high-charge electron beam being accelerated in quasi-linear plasma wakefields driven by a short proton beam. The structure of the studied wakefields are similar to those of a long, modulated proton beam, such as the AWAKE proton driver. We show that by properly choosing the electron beam parameters and exploiting two well known effects, beam loading of the wakefield and full blow out of plasma electrons by the accelerated beam, the electron beam can gain large amounts of energy with a narrow final energy spread (%-level) and without significant emittance growth. |
|
2017
|
A Rubidium Vapor Source for a Plasma Source for AWAKE
G. Plyushchev, R. Kersevan, A. Petrenko, P. Muggli
G. Plyushchev et al., Journal of Physics D: Applied Physics, 51(2), 025203 (2017).
Abstract:
We present the scheme for a rubidium vapor source that is used as a plasma source in the AWAKE plasma wakefield acceleration experiment. The plasma wakefield acceleration process requires a number of stringent parameters for the plasma: electron density adjustable in the (1-10)x1014cm-3 range, 0.25% relative density uniformity, sharp (<10cm) density ramps at each end, density gradient adjustable from -3 to +10% over 10m, and %-level density step near the beginning the plasma column. We show with analytical and direct Simulation Monte Carlo results that the rubidium density in the proposed source should meet these requirements. Laser ionization then transfers the above neutral vapor parameters to the plasma. |
|
2017
|
AWAKE readiness for the study of the seeded self-modulation of a 400GeV proton bunch
P. Muggli, for the AWAKE Collaboration
P. Muggli et al., Plasma Physics and Controlled Fusion, 60(1) 014046 (2017).
Abstract:
AWAKE is a proton-driven plasma wakefield acceleration experiment. We show that the experimental setup briefly described here is ready for systematic study of the seeded self-modulation of the 400GeV proton bunch in the 10\,m-long rubidium plasma with density adjustable from 1 to 10×1014cm−3. We show that the short laser pulse used for ionization of the rubidium vapor propagates all the way along the column, suggesting full ionization of the vapor. % We show that ionization occurs along the proton bunch, at the laser time and that the plasma that follows affects the proton bunch. |
|
2017
|
GHz Modulation detection using a streak camera: suitability of streak cameras in the AWAKE experiment
K. Rieger, A. Caldwell, O. Reimann, and P. Muggli
K. Rieger et al., Review of Scientific Instruments 88, 025110 (2017).
Abstract:
Using frequency mixing a modulated light pulse of ns duration is created. We show that, with a streak camera, we
can detect via an FFT detection approach up to 450 GHz modulation in a pulse in a single measurement, which is
an unusual application of a streak camera. This work is performed in the context of the AWAKE plasma wake eld
experiment where modulation frequencies in the range of 80-280 GHz are expected. |
|
2016
|
AWAKE: A Proton-Driven Plasma Wakefield Acceleration Experiment at CERN
C.Bracco and P. Muggli et al.
C.Bracco et al., Nuclear and Particle Physics Proceedings 273-275, 175 (2016).
Abstract:The AWAKE Collaboration has been formed in order to demonstrate proton-driven plasma wakefield acceleration for the first time. This acceleration technique could lead to future colliders of high energy but of a much reduced length when compared to proposed linear accelerators. The CERN SPS proton beam in the CNGS facility will be injected into a 10 m plasma cell where the long proton bunches will be modulated into significantly shorter micro-bunches. These micro-bunches will then initiate a strong wakefield in the plasma with peak fields above 1 GV/m that will be harnessed to accelerate a bunch of electrons from about 20 MeV to the GeV scale within a few meters. The experimental program is based on detailed numerical simulations of beam and plasma interactions. The main accelerator components, the experimental area and infrastructure required as well as the plasma cell and the diagnostic equipment are discussed in detail. First protons to the experiment are expected at the end of 2016 and this will be followed by an initial three-four years experimental program. The experiment will inform future larger-scale tests of proton-driven plasma wakefield acceleration and applications to high energy colliders. |
|
2016
|
Proton-Beam-Driven Plasma Acceleration
E. Adli and P. Muggli
E. Adli and P. Muggli, Rev. Accl. Sci. Tech. 09, 85 (2016).
Abstract:
We describe the main ideas, promises and challenges related to proton-driven plasma wakefield acceleration. Existing
high-energy proton beams have the potential to accelerate electron beams to the TeV scale in a single plasma stage.
In order to drive a wake effectively the available beams must be either highly compressed or microbunched. The
self-modulation instability has been suggested as a way to microbunch the proton beams. The AWAKE project at
CERN is currently the only planned proton-driven plasma acceleration experiment. A self-modulated CERN SPS
beam will be used to drive a plasma wake. We describe the design choices and experimental setup for AWAKE, and
discuss briefly the short-term objectives as well as longer-term ideas for the project. |
|
2016
|
Staging optics considerations for a plasma wakefield acceleration linear collider
C.A. Lindstrøm, E. Adli, J.M. Allen, J.P. Delahaye, M.J. Hogan, C. Joshi, P. Muggli, T.O. Raubenheimer, V. Yakimenko
C.A. Lindstrøm et al., Nucl. Instr. and Meth. in Phys. Res. A 829, 224 (2016).
Abstract:
Plasma wakefield acceleration offers acceleration gradients of several GeV/m, ideal for a next-generation linear collider. The beam optics requirements between plasma cells include injection and extraction of drive beams, matching the main beam beta functions into the next cell, canceling dispersion as well as constraining bunch lengthening and chromaticity. To maintain a high effective acceleration gradient, this must be accomplished in the shortest distance possible. A working example is presented, using novel methods to correct chromaticity, as well as scaling laws for a high energy regime. |
|
2016
|
An accurate Rb density measurement method for a plasma wakefield accelerator experiment using a novel Rb reservoir
E. Öz, F. Batsch, P. Muggli
E. Öz et al., Nucl. Instr. and Meth. in Phys. Res. A 829, 321 (2016).
Abstract:
A method to accurately measure the density of Rb vapor is described. We plan on using this method for the Advanced Wakefield (AWAKE) (Assmann et al., 2014 [1]) project at CERN , which will be the world׳s first proton driven plasma wakefield experiment. The method is similar to the hook (Marlow, 1967 [2]) method and has been described in great detail in the work by Hill et al. (1986) [3]. In this method a cosine fit is applied to the interferogram to obtain a relative accuracy on the order of 1% for the vapor density–length product. A single-mode, fiber-based, Mach–Zenhder interferometer will be built and used near the ends of the 10 meter-long AWAKE plasma source to be able to make accurate relative density measurement between these two locations. This can then be used to infer the vapor density gradient along the AWAKE plasma source and also change it to the value desired for the plasma wakefield experiment. Here we describe the plan in detail and show preliminary results obtained using a prototype 8 cm long novel Rb vapor cell. |
|
2016
|
Laser pulse propagation in a meter scale rubidium vapor/plasma cell in AWAKE experiment
A. Joulaei, J. Moody, N. Berti, J. Kasparian, S. Mirzanejhad, P. Muggli
A. Joulaei et al., Nucl. Instr. and Meth. in Phys. Res. A 829, 339 (2016).
Abstract:
We present the results of numerical studies of laser pulse propagating in a 3.5 cm Rb vapor cell in the linear dispersion regime by using a 1D model and a 2D code that has been modified for our special case. The 2D simulation finally aimed at finding laser beam parameters suitable to make the Rb vapor fully ionized to obtain a uniform, 10 m-long, at least 1 mm in radius plasma in the next step for the AWAKE experiment. |
|
2016
|
AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN
E. Gschwendtner et al.
E. Gschwendtner et al., Nucl. Instr. and Meth. in Phys. Res. A 829, 76 (2016).
Abstract:
The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented. |
|
2014
|
Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam
K. V. Lotov, A. P. Sosedkin, A. V. Petrenko, L. D. Amorim, J. Vieira, R. A. Fonseca, L. O. Silva, E. Gschwendtner and P. Muggli
K. V. Lotov et al., Phys. Plasmas 21, 123116 (2014).
Abstract:
It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating
particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail
part of the driver, since the plasma wave phase velocity there can exceed the light velocity,
which is necessary for efficient acceleration. If the witness beam is many wakefield periods long,
then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons,
but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient
trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than
several centimeters. Positrons are not susceptible to the initial plasma density gradient. |
|
2014
|
High-efficiency acceleration of an electron beam in a plasma wakefield accelerator
M. Litos, E. Adli, W. An, C. I. Clarke, C. E. Clayton, S. Corde, J. P. Delahaye, R. J. England, A. S. Fisher, J. Frederico, S. Gessner, S. Z. Green, M. J. Hogan, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, N. Vafaei-Najafabadi, D. Walz, G. White, Z. Wu, V. Yakimenko, G. Yocky
M. Litos et al., Nature 515, 92 (2014).
Abstract:
High-efficiency acceleration of charged particle beams at high gradients of energy gain per unit length is necessary
to achieve an affordable and compact high-energy collider. The plasma wakefield accelerator is one concept
being developed for this purpose. In plasma wakefield acceleration, a charge-density wake with high accelerating
fields is driven by the passage of an ultra-relativistic bunch of charged particles (the drive bunch) through a plasma.
If a second bunch of relativistic electrons (the trailing bunch) with sufficient charge follows in the wake of
the drive bunch at an appropriate distance, it can be efficiently accelerated to high energy. Previous experiments
using just a single 42-gigaelectronvolt drive bunch have accelerated electrons with a continuous energy spectrum and
a maximum energy of up to 85 gigaelectronvolts from the tail of the same bunch in less than a metre of plasma.
However, the total charge of these accelerated electrons was insufficient to extract a substantial amount of energy
from the wake. Here we report high-efficiency acceleration of a discrete trailing bunch of electrons that contains
sufficient charge to extract a substantial amount of energy from the high-gradient, nonlinear plasma wakefield accelerator.
Specifically, we show the acceleration of about 74 picocoulombs of charge contained in the core of the trailing bunch in an
accelerating gradient of about 4.4 gigavolts per metre. These core particles gain about 1.6 gigaelectronvolts of energy
per particle, with a final energy spread as low as 0.7 per cent (2.0 per cent on average), and an energy-transfer
efficiency from the wake to the bunch that can exceed 30 per cent (17.7 per cent on average). This acceleration of
a distinct bunch of electrons containing a substantial charge and having a small energy spread with both a high
accelerating gradient and a high energy-transfer efficiency represents a milestone in the development of plasma
wakefield acceleration into a compact and affordable accelerator technology. |
|
2014
|
Laser Ionized Preformed Plasma at FACET
S Z Green, E. Adli, C.I. Clarke, S. Corde, S.A. Edstrom, A.S. Fisher, J. Frederico, J.C. Frisch, S. Gessner, S. Gilevich, P. Hering, M.J. Hogan, R.K. Jobe, M. Litos, J.E. May, D.R. Walz, V. Yakimenko, C.E. Clayton, C. Joshi, K.A. Marsh, N. Vafaei-Najafabadi, P. Muggli
S.Z. Green et al., Plasma Phys. Control. Fusion 56, 084011 (2014).
Abstract:
The Facility for Advanced Accelerator and Experimental Tests (FACET) at SLAC installed a 10-TW Ti:Sapphire
laser system for pre-ionized plasma wakefield acceleration experiments. High energy (500 mJ), short (50 fs)
pulses of 800-nm laser light at 1 Hz are used at the FACET experimental area to produce a plasma column.
The laser pulses are stretched to 250 fs before injection into a vapor cell, where the laser is focused
by an axicon lens to form a plasma column that can be sustained over the desired radius and length.
A 20-GeV electron bunch interacts with this preformed plasma to generate a non-linear wakefield,
thus accelerating a trailing witness bunch with gradients on the order of several GV/m.
The experimental setup and methods for producing the pre-ionized plasma for plasma wakefield acceleration
experiments performed at FACET are described. |
|
2014
|
Self-modulation instability of ultra-relativistic particle bunches with finite rise times
J. Vieira, L.D. Amorim, Y. Fang, W.B.Mori, P. Muggli, L.O. Silva
J. Vieira et al., Plasma Phys. Control. Fusion 56, 084014 (2014).
Abstract:
We study the evolution of the self-modulation instability using bunches with rise times longer than the
plasma wavelength. Using particle-in-cell simulations we show that unlike long bunches with sharp rise times,
there are large variations of the wake amplitudes and wake phase velocity before self-modulation instability saturation.
These results show that use of bunches with sharp rise times is important to seed the self-modulation instability
to ensure stable acceleration regimes. |
|
2014
|
Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics
AWAKE Collaboration: R. Assmann, R. Bingham, T. Bohl, C. Bracco, B. Buttenschön, A. Butterworth, A. Caldwell, S. Chattopadhyay, S. Cipiccia, E. Feldbaumer, R.A. Fonseca, B. Goddard, M. Gross, O. Grülke, E. Gschwendtner, J. Holloway,
C. Huang, D. Jaroszynski, S. Jolly, P. Kempkes, N. Lopes, K. Lotov, J. Machacek, S.R. Mandry, M. Meddahi, N. Moschuering, P. Muggli, Z. Najmudin, P. A. Norreys, E. Oz, A. Pardons, A. Petrenko, A. Pukhov, K. Rieger,
O. Reimann, H. Ruhl, E. Shaposhnikova, L.O. Silva, A. Sosedkin, R. Tarkeshian, R.M.G.N. Trines, T. Tückmantel, J. Vieira, H. Vincke, M. Wing, G. Xia
AWAKE Collaboration, Plasma Phys. Control. Fusion 56 084013 (2014), available at arXiv:1401.4823.
Abstract:
New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas.
Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons
accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale
in a single stage. An experimental program at CERN - the AWAKE experiment - has been launched to study in detail the important physical processes and to demonstrate the power of
proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wake field accelerator. |
|
2014
|
Hosing Instability Suppression in Self-modulated Plasma Wakefields
J. Vieira, W.B. Mori and P. Muggli
J. Vieira et al., Phys. Rev. Lett. 112, 205001 (2014).
Abstract:
We show that hosing of a long particle beam is stabilized for a beam that is 100% self-modulated if
the associated plasma density perturbation is linear. These results indicate that when a train of
particle bunches or laser pulses excite a linear wake, the train is stable against hosing.
We derive scalings for maximum bunch tilts and SMI seeds needed to ensure stable propagation
beyond saturation of the self-modulation instability. Numerical solutions of the reduced
hosing equations and three-dimensional particle-in-cell simulations confirm our analytical findings. |
|
2014
|
|
2014
|
A novel Rb vapor plasma source for plasma wakefield accelerators
E. Oz and P. Muggli
E. Oz et al., Nucl. Instr. Meth. Phys. Res. A 740(11), 197 (2014).
Abstract:
We describe a novel plasma source developed at the Max Planck Institute for Physics that will be
used for a proton driven plasma wakefield accelerator experiment at CERN.
Rubidium vapor is confined in a 10 meter-long, 4 cm diameter, oil-heated stainless steel pipe.
A laser pulse tunnel ionizes the vapor forming a 10-meter long, radius plasma with a range of densities around .
Access to the source is provided using custom manufactured fast valves. The source is designed to produce a plasma
with a density uniformity of at least 0.2% during the beam–plasma interaction. |
|
2014
|
The effect of plasma radius and profile on the development of self-modulation instability of electron bunches
Y. Fang, L.D. Amorim, J. Vieira, W.B. Mori and P. Muggli
Y. Fang et al., Phys. Plasmas 21, 056703 (2014).
Abstract:
Plasmas available for PWFA experiments may have longitudinal and transverse density profiles that could
affect the outcome of an experiment. This paper investigates the effect of plasmas with finite radius and
inhomogeneous transverse density profiles on the wakefield excitation and the self-modulation instability (SMI)
development in overdense plasmas. We focus here on the case of an electron bunch. Simulation results show that
such plasmas generate larger focusing force for the propagating electron beam, and therefore higher growth rate
for the SMI. Although the initial Ez amplitude is lower in such plasmas, the increased focusing force can dominate
the development trend of the SMI, i.e., larger saturated Ez amplitude can be reached over similar plasma lengths. |
|
2014
|
Seeding of the Self-modulation Instability of a long Electron Bunch in a Plasma
Y. Fang, V. E. Yakimenko, M. Babzien, M. Fedurin, K. P. Kusche, R. Malone, J. Vieira, W.B. Mori and P. Muggli
Y. Fang et al., Phys. Rev. Lett. 112, 045001 (2014).
Abstract:
We demonstrate experimentally that a relativistic electron bunch shaped with a sharp rising edge drives plasma wakefields with one to seven periods
along the bunch as the plasma density is increased. The plasma density is varied in the 1015-1017 cm-3 range.
The wakefields generation is observed after the plasma as periodic modulation of the correlated energy spectrum of the incoming bunch.
We choose a low bunch charge of 50 pC for optimum visibility of the modulation at all plasma densities.
The longitudinal wakefields creating the modulation are in the MV/m range and are indirect evidence of the
generation of transverse wakefields that can seed the self-modulation instability, although the instability
does not grow significantly over the short plasma length (2 cm). We show that the seeding provides a phase
reference for the wakefields, a necessary condition for the deterministic external injection of a witness bunch
in an accelerator. This electron work supports the concept of similar experiments in the future, e.g. SMI experiments
using long bunches of relativistic protons. |
|
2014
|
Beam loading by distributed injection of electrons in a plasma wakefield accelerator
N. Vafaei-Najafabadi, K. A. Marsh, C. E. Clayton, W. An, W. B. Mori, C. Joshi, W. Lu, E. Adli, S. Corde, M. Litos, S. Li, S. Gessner, J. Frederico, A. S. Fisher, Z. Wu, D. Walz, R. J. England, J. P. Delahaye, C. I. Clarke, M. J. Hogan, and P. Muggli
N. Vafaei-Najafabadi et al., Phys. Rev. Lett. 112, 025001 (2014).
Abstract:
We show through experiments and supporting simulations that propagation of a highly relativistic and dense
electron bunch through a plasma can lead to distributed injection of electrons, which depletes the accelerating field;
i.e. beam loads the wake. The source of the injected electrons is ionization of the second electron of rubidium (Rb II)
within the wake. This injection of excess charge is large enough to severely beam load the wake, and thereby reduce the
transformer ratio T. The reduction of the average T with increasing beam loading is quantified for the first time by
measuring the ratio of peak energy gain and loss of electrons while changing the beam emittance. Simulations show that
beam loading by RbII electrons contributes to the reduction of the peak accelerating field from its weakly loaded value
of 43 GV/m to strongly loaded value of 26 GV/m. |
|
2013
|
Interaction of Ultra Relativistic e- e+ Fireball Beam with Plasma
P. Muggli, S.F. Martins, J. Vieira, L. O. Silva
P. Muggli et al., arXiv:1306.4380 (2013).
Abstract:
Ab initio simulations of the propagation in a plasma of a soon to be available relativistic electron-positron
beam or fireball beam provide an effective mean for the study of microphysics relevant to astrophysical scenarios.
We show that the current filamentation instability associated with some of these scenarios reaches saturation after
only 10 cm of propagation in a typical laboratory plasma with a density 1017/cc. The different regimes of the
instability, from the purely transverse to the mixed mode filamentation, can be accessed by varying the background
plasma density. The instability generates large local plasma gradients, intense transverse magnetic fields,
and enhanced emission of radiation. We suggest that these effects may be observed experimentally for the first time. |
|
2013
|
Strategies for mitigating the ionization-induced beam head erosion problem in an electron-beam-driven plasma wakefield accelerator
W. An, M. Zhou, N. Vafaei-Najafabadi, K. A. Marsh, C. E. Clayton, C. Joshi, W. B. Mori, W. Lu, E. Adli, S. Corde, M. Litos, S. Li, S. Gessner, J. Frederico, M. J. Hogan, D. Walz, J. England, J. P. Delahaye, and P. Muggli
W. An et al., Phys. Rev. ST Accel. Beams 16, 101301 (2013).
Abstract:
Strategies for mitigating ionization-induced beam-head erosion in an electron-beam-driven plasma wake field accelerator (PWFA)
are explored when the plasma and the wake are both formed by the transverse electric field of the beam itself. Beam head erosion can occur
in a preformed plasmas because of a lack of focusing force from the wake at the rising edge (head) of the beam due to the finite inertia of
the electrons. When the plasma is produced by field ionization from the space charge field of the beam, the head erosion is significantly
exacerbated due to the gradual recession (in the beam frame) of the 100% ionization contour. Beam particles in front of the ionization
front cannot be focused (guided) causing them to expand as in vacuum. When they expand, the location of the ionization front recedes such
that even more beam particles are completely unguided. Eventually this process terminates the wake formation prematurely, i.e., well
before the beam is depleted of its energy. Ionization-induced head erosion can be mitigated by controlling the beam parameters
(emittance, charge and energy) and/or the plasma conditions. In this paper we explore how the latter can be optimized so as to extend
the beam propagation distance and thereby increase the energy gain. In particular we show that, by using a combination of the alkali
atoms of the lowest practical ionization potential (Cs) for plasma formation and a precursor laser pulse to generate a narrow plasma filament
in front of the beam, the head erosion rate can be dramatically reduced. Simulation results show that in the upcoming ``two-bunch PWFA experiments"
on the FACET facility at SLAC national accelerator laboratory the energy gain of the trailing beam can be up to 10 times larger for
the given parameters when employing these techniques. Comparison of the effect of beam head erosion in preformed and ionization produced
plasmas is also presented. |
|
2012
|
Experimental Study of Current Filamentation Instability
B. Allen, V. Yakimenko, M. Babzien, M. Fedurin, K. Kusche, P. Muggli
B. Allen et al., Phys. Rev. Lett. 109, 185007 (2012).
Abstract:
Current filamentation instability is observed and studied in a laboratory environment with a 60MeV electron beam and a plasma capillary discharge. Multiple filaments are observed and imaged transversely at the plasma exit with
optical transition radiation. By varying the plasma density the transition between single and multiple filaments is found to be kpσr~2.2. Scaling of the transverse filament size with the plasma skin depth
is predicted in theory and observed over a range of plasma densities. Lowering the bunch charge, and thus bunch density, suppresses the instability. |
|
2012
|
Experimental observation of suppressing CSR-induced beam energy spread with shielding plates
V. Yakimenko, M. Fedurin, V. Litvinenko, A. Fedotov, D. Kayran, P. Muggli
V. Yakimenko et al., Phys. Rev. Lett. 109, 164802 (2012).
Abstract:
We describe the first direct observation of the significant suppression of the energy spread induced by coherent synchrotron radiation (CSR) by a pair of conductive plates placed inside a dipole magnet. In addition to various feedback loops
improving the energy stability of the beam parameters, our key innovation for this experiment is the observation of the time-resolved energy-variation within the electron bunch, instead of the traditionally measured RMS energy spread. We present
the results of the experiments and compare them with a rigorous analytical theory. |
|
2012
|
Dielectric wakefield acceleration of a relativistic electron beam in a slab-symmetric dielectric lined waveguide
G. Andonian, D. Stratakis, O. Williams, B. O’Shea, X. Wei, E. Hemsing, P. Muggli, M. Babzien, K. Kusche, M. Fedurin, V. Yakimenko, J.B. Rosenzweig
G. Andonian et al., Phys. Rev. Lett. 108, 244801 (2012).
Abstract:
We report first evidence of wakefield acceleration of a relativistic electron beam in a dielectric-lined slab-symmetric structure. The high energy tail of a 60 MeV electron beam was accelerated by 150 keV in a 2cm long,
slab-symmetric SiO2 waveguide, with the acceleration/deceleration clearly visible due to use of a beam with a bifurcated longitudinal distribution that serves to approximate well a driver-witness beam pair.
This split-bunch distribution is verified by longitudinal reconstruc- tion analysis of the emitted coherent transition radiation. The dielectric waveguide structure is further characterized by spectral analysis
of the emitted coherent Cerenkov radiation at THz frequencies, from a single electron bunch, and from a a relativistic bunch train with spacing selectively tuned to the second longitudinal mode (TM02).
Start-to-end simulation results reproduce aspects of the electron beam bifurcation dynamics, emitted THz radiation properties, and the observation of acceleration in the dielectric lined,
slab-symmetric waveguide. |
|
2012
|
A proposed demonstration of an experiment of proton-driven plasma wakefield acceleration based on CERN SPS
G. Xia, R. Assmann, R. A. Fonseca, C. Huang, W. Mori, L. O. Silva, J. Vieira, F. Zimmermann and P. Muggli
G. Xia et al., J. Plasma Phys., 1-7 (2012).
Abstract:
The proton bunch-driven plasma wakefield acceleration (PWFA) has been proposed as an approach to accelerate an electron beam to the TeV energy regime in a single plasma section.
An experimental program has been recently proposed to demonstrate the capability of proton-driven PWFA by using existing proton beams from the European Organization for Nuclear Research (CERN)
accelerator complex. At present, a spare Super Proton Synchrotron (SPS) tunnel, having a length of 600 m, could be used for this purpose. The layout of the experiment is introduced.
Particle-in-cell simulation results based on realistic SPS beam parameters are presented. Simulations show that working in a self-modulation regime, the wakefield driven by an SPS beam
can accelerate an externally injected approx. 10 MeV electrons to approx. 2 GeV in a 10-m plasma, with a plasma density of 7x1014 cm-3. |
|
2012
|
Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator
J. Vieira, Y. Fang, W.B. Mori, L. O. Silva and P. Muggli
J. Vieira et al., Phys. Plasmas 19, 063105 (2012).
Abstract:
The transverse self-modulation of ultra-relativistic, long lepton bunches in high-density plasmas is explored through
full-scale particle-in-cell simulations. We demonstrate that long SLAC-type electron and positron bunches can become strongly
self-modulated over centimeter distances, leading to wake excitation in the blowout regime with accelerating fields in excess
of 20 GV/m. We show that particles energy variations exceeding 10 GeV can occur in meter-long plasmas. We find that the
self-modulation of positively and negatively charged bunches differ when the blowout is reached. Seeding the self-modulation
instability mitigates the effect of the competing hosing instability. This work reveals that a proof-of-principle experiment to
test the physics of bunch self-modulation can be performed with available lepton bunches and with existing experimental apparatus
and diagnostics. |
|
2011
|
Teravolt-per-meter beam and plasma fields from low-charge femtosecond electron beams
J.B. Rosenzweig, G. Andonian, P. Bucksbaum, M. Ferrario, S. Full, A. Fukusawa, E. Hemsing, B. Hidding, M. Hogan, P. Krejcik, P. Muggli, G. Marcus, A. Marinelli, P. Musumeci, B. O'Shea, C. Pellegrini, D. Schiller, G. Travish
J.B. Rosenzweig et al., Nucl. Inst. Meth. Phys. Res. A 663(1), 98 (2011).
Abstract:
Recent initiatives in ultra-short, GeV electron beam generation have been aimed at achieving sub-femtosecond (fs) pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode.
This scheme foresees the use of very low charge beams, which may allow existing FEL injectors to produce few-100 as pulses, with very high brightness. Towards this end, recent experiments at SLAC have produced
approximately 2 fs rms, low transverse emittance, 20 pC electron pulses. Here we examine the use of such pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator.
We present a scheme for focusing the beam to very small dimensions, where the surface Coulomb fields are also at the TV/m level. These conditions access a new regime for high field for atomic physics,
allowing frontier atomic physics experiments such as barrier suppression regime ionization. They also, critically, permit well-sub-fs plasma formation for subsequent wake excitation.
We examine the use of such ultra-short beams for creating coherent sub-cycle IR radiation at unprecedented high power levels. |
|
2011
|
Phase Velocity and Particle Injection in a Self-Modulated Proton-Driven Plasma Wakefield Accelerator
A. Pukhov, N. Kumar, T. Tuckmantel, A. Upadhyay, K. Lotov, P. Muggli, V. Khudik, C. Siemon, and G. Shvets
A. Pukhov et al., Phys. Rev. Lett. 107, 145003 (2011).
Abstract:
It is demonstrated that the performance of the self-modulated proton driver plasma wakefield accelerator is strongly affected by the reduced phase velocity of the plasma wave.
Using analytical theory and particle-in-cell simulations, we show that the reduction is largest during the linear stage of self-modulation.
As the instability nonlinearly saturates, the phase velocity approaches that of the driver.
The deleterious effects of the wake’s dynamics on the maximum energy gain of accelerated electrons can be avoided using side-injections of electrons,
or by controlling the wake’s phase velocity by smooth plasma density gradients. |
|
2011
|
Resonant Excitation of Coherent Cerenkov Radiation in Dielectric Lined Waveguides
G. Andonian, O. Williams,1 X. Wei, P. Niknejadi, E. Hemsing, J.B. Rosenzweig, P. Muggli, M. Babzien, M. Fedurin, K. Kusche, R. Malone, and V. Yakimenko
G. Andonian et al., Appl. Phys. Lett. 98, 202901 (2011).
Abstract:
We report the observation of coherent Cerenkov radiation in the terahertz regime emitted by a relativistic electron pulse train passing through a
dielectric lined cylindrical waveguide. We describe the beam manipulations and measurements involved in repetitive pulse train creation including comb
collimation and nonlinear optics corrections. With this technique, modes beyond the fundamental are selectively excited by use of the appropriate frequency train.
The spectral characterization of the structure shows preferential excitation of the fundamental and of a higher longitudinal mode. |
|
2011
|
Hollow plasma channel for positron plasma wakefield acceleration
W. D. Kimura, H. M. Milchberg P. Muggli, X. Li, W. B. Mori
W. D. Kimura et al., Phys. Rev. ST Accel. Beams 14, 041301 (2011).
Abstract:
Plasma wakefield acceleration (PWFA) has demonstrated the ability to produce very high gradients to accelerate electrons and positrons. In PWFA, a drive bunch of charged particles passes through a uniform plasma,
thereby generating a wakefield that accelerates a witness bunch traveling behind the drive bunch. This process works well for electrons, but much less so for positrons due to the positive charge attracting rather than
repealing the plasma electrons, which leads to reduced acceleration gradient, halo formation, and emittance growth. This problem can be alleviated by having the positron beam travel through a hollow plasma channel.
Presented are modeling results for producing 10-100 cm long hollow plasma channels suitable for positron PWFA. These channels are created utilizing laser-induced gas breakdown in hydrogen gas. The results show that
hollow channels with plasma densities of order 1016cm-3 and inner channel radii of order 20μm are possible using currently available terawatt-level lasers. At these densities and radii, preliminary positron PWFA
modeling indicates that longitudinal electric fields on axis can exceed 3GV/m. |
|
2011
|
Effect of temperature on ion motion in future plasma wakefield accelerators
R. Gholizadeh, T. Katsouleas, C. Huang, W. B. Mori and P. Muggli
R. Gholizadeh et al., Phys. Rev. ST Accel. Beams 14, 021303 (2011).
Abstract:
We study the effect of plasma temperature on ion motion in a plasma wakefield accelerator with parameters typical of a future high-energy accelerator. We show that the collapse of the plasma ions caused by the extremely high fields of ultra-dense electron bunches can be prevented only by a very high plasma ion temperature. |
|
2010
|
Scaling of the longitudinal electric field and transformer ratio in a nonlinear plasma wakefield accelerator
I. Blumenfeld, C. E. Clayton, F. J. Decker, M. J. Hogan, C. Huang, R. Ischebeck, R. H. Iverson, C. Joshi, T. Katsouleas, N. Kirby, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, E. Oz, R. H. Siemann, D. R. Walz, and M. Zhou
I. Blumenfeld et al., Phys. Rev. ST Accel. Beams 13, 111301 (2010).
Abstract:
The scaling of the two important figures of merit, the transformer ratio, T, and the longitudinal electric field, Ez,
with the peak drive-bunch current, IP, in a nonlinear Plasma Wakefield Accelerator is presented for the first time.
The longitudinal field scales as IP0.623+/-0.007, in good agreement with nonlinear wakefield theory (IP0.5), while the unloaded
transformer ratio is shown to be greater than unity and scales weakly with the bunch current. The effect of bunch head
erosion on both parameters is also discussed. |
|
2010
|
A Simple Method for Generating Adjustable Trains of Picosecond Electron Bunches
P. Muggli, B. Allen, V. E. Yakimenko, J. Park, M. Babzien, K. P. Kusche, W.D. Kimura
P. Muggli et al., Phys. Rev. ST Accel. Beams 13, 052803 (2010).
Abstract:
A simple, passive method for producing an adjustable train of picosecond electron bunches is demonstrated.
The key component of this method is an electron beam mask consisting of an array of parallel wires that selectively
spoils the beam emittance. This mask is positioned in a high magnetic dispersion, low beta-function region of the beam line.
The incoming electron beam striking the mask has a time/energy correlation that corresponds to a time/position
correlation at the mask location. The mask pattern is transformed into a time pattern or train of bunches when
the dispersion is brought back to zero downstream of the mask. Results are presented of a proof-of-principle
experiment demonstrating this novel technique that was performed at the Brookhaven National Laboratory Accelerator Test Facility.
This technique allows for easy tailoring of the bunch train for a particular application, including varying
the bunch width and spacing, and enabling the generation of a trailing witness bunch. |
|
2010
|
Plasma Wakefield Acceleration Experiments at FACET
M.J. Hogan, T. O. Raubenheimer, A. Seryi, P. Muggli, T. Katsouleas, C. Huang, W. Lu, W. An, K.A. Marsh, W.B. Mori, C. E. Clayton, C. Joshi
M.J. Hogan et al., New J. Phys. 12, 055030 (2010).
Abstract:
FACET Facilities for Accelerator science and Experimental Test beams at SLAC will
provide high energy density electron and positron beams with peak currents of roughly
20 kA that will be focused down to a 10μm x 10μm transverse spot size at an energy of
~23 GeV. With FACET, the SLAC linac will support a unique program concentrating on
second-generation research in plasma wakefield acceleration. Topics include high-
gradient electron acceleration with a narrow energy spread and preserved emittance,
beam loading, and high-gradient positron acceleration. This paper describes the FACET
facility, summarizes the state of the art for plasma wakefield accelerators and discusses
the plasma wakefield accelerator program to be conducted at FACET over the next five
years. |
|
2010
|
Energy Gain Scaling with Plasma Length and Density in the Plasma Wakefield Accelerator
P. Muggli, I. Blumenfeld, C. E. Clayton, F. J. Decker, M. J. Hogan, C. Huang, R. Ischebeck, R. H. Iverson, C. Joshi, T. Katsouleas, N. Kirby, W. Lu, K. A. Marsh, W. B. Mori, E. Oz, R. H. Siemann, D. R. Walz, M. Zhou
P. Muggli et al., New J. Phys. 12, 045022 (2010).
Abstract:
We present plasma wakefield acceleration experimental results showing that the energy gain by 28.5~GeV
electrons scales with plasma length, and reaches 14 GeV over a plasma with a density of 2.6x1017cm-3
and a length of 31 cm. At this plasma density the average accelerating gradient is 36 GV/m.
These results are in good agreements with the numbers obtained from particle in cell simulations describing the experiment.
The linear scaling is also observed both at lower and higher plasma densities, at which smaller energy gains and accelerating
gradients are measured. The systematic measurements of energy gain show the reproducibility and control of the acceleration process. |
|
2010
|
Preservation of beam emittance in the presence of ion motion in future plasma wakefield-based colliders
R. Gholizadeh, T. Katsouleas, P. Muggli, C. Huang, W. Mori
R. Gholizadeh et al., Phys. Rev. Lett. 104, 155001 (2010).
Abstract:
The preservation of beam quality in a plasma wakefield accelerator driven by ultra high intensity
and ultra low emittance beams, characteristic of future particle colliders, is a challenge.
The electric field of these beams leads to plasma ions motion, resulting in a nonlinear focusing force
and emittance growth of the beam. We propose to use an adiabatic matching section consisting of a short
plasma section with a decreasing ion mass to allow for the beam to remain matched to the focusing force.
We use analytical models and numerical simulations to show that the emittance growth can be significantly reduced |
|
2009
|
Optimization of Positron Trapping and Acceleration in an Electron-beam-driven Plasma Wakefield Accelerator
X. Wang, P. Muggli, T. Katsouleas, C. Joshi, W. B. Mori, R. Ischebeck, M. J. Hogan
X. Wang et al., Phys. Rev. ST Accel. Beams 12, 051303 (2009).
Abstract: Positron trapping and acceleration
in a plasma wake using a four-bunch scheme [X. Wang et al., Phys. Rev. Lett. 101, 124801 (2008)]
is numerically investigated through 2D particle-in-cell simulations. This scheme that integrates
positron generation, trapping and acceleration into a single stage is a promising approach for
positron acceleration in a future plasma-based linear collider. It consists of a plasma with an
embedded thin foil target into which two closely spaced electron beams are shot.
The first beam creates a region for accelerating and focusing positrons and the second
beam provides positrons to be accelerated. Some of the outstanding issues related to the
quality of the accelerated positron beam load are discussed as a function of the beam and
plasma parameters. Simulations show that a large number of positrons (107 ~ 108) can be
trapped when the plasma wake is modestly nonlinear, and the positron-generating foil target
is immersed in the plasma. Beam loading can reduce the energy spread of the positron beam load.
The quality of the positron beam load is not very sensitive to the exact bunch spacing between
the drive electron bunch and the positron beam load. |
|
2009
|
Enhancing parallel quasi-static particle-in-cell simulations with a pipelining algorithm
B. Feng, C. Huang, V. Decyk, W. B. Mori, P. Muggli, T. Katsouleas
B. Feng et al., Journal of Computational Physics, 228(15), 5340 (2009).
Abstract: A pipelining algorithm is described
to overcome the limitation on scaling quasi-static particle-in-cell models of relativistic beams in plasmas
to a very large number of processors. The pipelining algorithm uses multiple groups of processors and optimizes
the job allocation on the processors in parallel computing. The algorithm is implemented on the quasi-static
code QuickPIC and is shown to scale to over 103 processors and increased the scale and speed by two orders of
magnitude over the non-pipelined model. The new approach opens the door to performing full scale 3-D simulations
of future plasma wakefield accelerators or full lifetime models of beam interaction with electron clouds
in circular accelerators such as the Large Hadron Collider (LHC) at CERN. |
|
2009
|
Review of High-energy Plasma Wakefield Experiments
Patric Muggli and Mark J. Hogan
P. Muggli and M.J. Hogan, Comptes Rendus Physique, 10(2-3), 116 (2009).
Abstract: Plasma wakefield accelerator (PWFA)
experiments have made considerable progress in the past decade by using high-energy particle beams to drive
large amplitude waves or wakes in a plasma. Electron beam driven experiments have measured the integrated
and dynamic aspects of plasma focusing, the bright flux high-energy of betatron radiation photons,
particle beam refraction at the plasma/neutral gas interface, and the structure and amplitude
of the accelerating wakefield. Gradients spanning kT/m to MT/m for focusing and 100 MeV/m to 50 GeV/m
for acceleration have been excited in plasmas with densities of 1014 to 1017 cm-3, respectively.
The large accelerating gradient led to the energy doubling of 42 GeV electrons in only 85 cm of plasma.
Positron beam driven experiments have evidenced the comparatively more complex dynamic and integrated plasma
focusing, the subsequent halo formation and emittance growth in the positron beam and demonstrated
accelerating gradients of nearly 100 MeV/m. This paper summarizes these experimental progress,
illustrates the key enabling technologies that made the work possible, concludes with a brief discussion
of proposed future directions, and suggests that the PWFA could one day revolutionize e-/e+ linear colliders. |
|
2009
|
Transverse Emittance and Current of Multi-GeV Trapped Electrons in a Plasma
Wakefield Accelerator
N. Kirby, I. Blumenfeld, C.E. Clayton, F.J. Decker, M.J. Hogan, C. Huang,
R. Ischebeck, R.H. Iverson, C. Joshi, T. Katsouleas, W. Lu, K.A. Marsh, S.F.
Martins, W.B. Mori, P. Muggli, E. Oz, R.H. Siemann, D.R. Walz, and M. Zhou
N. Kirby et al., Phys. Rev. ST Accel. Beams 12, 051302 (2009).
Abstract: Multi-GeV trapped electron bunches in a plasma wakefield accelerator (PWFA) are observed with
normalized transverse emittance divided by peak current, εN,x /It, below the level of 0.2 μm/kA. A
theoretical model of the trapped electron emittance, developed here, indicates that emittance scales
inversely with the square root of the plasma density in the nonlinear “bubble” regime of the PWFA.
This model and simulations indicate that the observed values of εN,x /It result from multi-GeV
trapped electron bunches with emittances of a few μm and multi-kA peak currents. |
|
2009
|
A High Density Hydrogen-Based Capillary Plasma Source for Particle-Beam-Driven Wakefield Accelerator Applications
Hao Chen, Efthymios Kallos, Patric Muggli, Thomas C. Katsouleas and Martin A. Gundersen
H. Chen et al., IEEE Trans. Plasma Sci. 37(3), 456 (2009).
Abstract: We report the generation of variable plasma
densities up to 1019 cm-3 in hydrogen-filled, hollow cathode
capillary discharges, and consider their applications as a practical
plasma source for particle-beam-driven plasma wakefield
accelerators. The capillary consists of a transparent, cylindrical
borosilicate glass tube. The plasma density is determined as a
function of time, using Stark broadening of the Hα line, with a
resolution of 50 ns, and is found to decay exponentially with a
typical time constant of several hundreds of nanoseconds. The
time delay between the discharge and the drive electron beam can
therefore be tuned to reach the density appropriate for the
maximum acceleration gradient. The dependence of the plasma
density on the capillary geometry and gas pressure is discussed,
and the results of optical studies of the discharge channel
formation process are presented. Implications of the results for
beam-driven plasma accelerators are discussed. |
|
2008
|
Positron Injection and Acceleration on the Wake Driven by an Electron Beam in a Foil and Gas Plasma
X. Wang, R.Ischebeck, P. Muggli, T. Katsouleas, C. Joshi, W. B. Mori, M. J. Hogan
X. Wang et al., Phys. Rev. Lett. 101, 124801 (2008).
Abstract: A novel approach for generating and accelerating positron bunches in a plasma
wake is proposed and modeled. The system consists of a plasma with an embedded thin
foil into which two electron beams are shot. The first beam creates a region for
accelerating and focusing positrons and the second beam provides positrons to be
accelerated. Monte Carlo and 3D PIC simulations show a large number of positrons
(107~108) are trapped and accelerated to ~5 GeV over 1 meter with relatively narrow
energy spread and low emittance. |
|
2008
|
Generation of Trains of Electron Microbunches with Adjustable Sub-picosecond Spacing
P. Muggli, V. Yakimenko, M. Babzien, E. Kallos, K. P. Kusche
P. Muggli et al., Phys. Rev. Lett. 101, 054801 (2008).
Abstract: We demonstrate that trains of
subpicosecond electron microbunches, with subpicosecond spacing, can be produced by placing a mask in a region of the beam line where the beam
transverse size is dominated by the correlated energy spread. We show that the number, length, and spacing of the microbunches can be controlled
through the parameters of the beam and the mask. Such microbunch trains can be further compressed and accelerated, and have applications
to free electron lasers (FELs) and plasma wakefield accelerators (PWFAs). |
|
2008
|
Halo Formation and Emittance Growth of Positron Beams in Plasmas
P. Muggli, B.E. Blue, C.E. Clayton, F.J. Decker, M.J. Hogan, C. Huang, C. Joshi, T.C. Katsouleas, W. Lu, W.B. Mori, C.L. O'Connell, R.H. Siemann, D. Walz, M. Zhou
P. Muggli et al., Phys. Rev. Lett. 101, 055001 (2008).
Abstract: An ultra-relativistic 28.5 GeV,
700 μm-long positron bunch is focused near the entrance of a 1.4m-long plasma with a density
ne between ~1013 cm-3 and 5x1014 cm-3. Partial neutralization
of the bunch space charge by the mobile plasma electrons results in a reduction in transverse size by
a factor of ~3 in the high emittance plane of the beam ~1 m downstream from the plasma exit.
As ne increases the formation of a beam halo containing ~40% of the total charge is observed,
indicating that the plasma focusing force is nonlinear. Numerical simulations confirm these observations.
The bunch with an incoming transverse size ratio of ~3 and emittance ratio of ~5 suffers
emittance growth and exits the plasma with approximately equal sizes and emittances. |
|
2008
|
Gigavolt per Meter Breakdown Limits on Wakefields Driven by Electron Beams in Dielectric Structures
M. C. Thompson, H. Badakov, A. M. Cook, J.B. Rosenzweig, R. Tikhoplav, G. Travish, I. Blumenfeld, M.J. Hogan, R. Ischebeck, N. Kirby, R. Siemann, D. Walz, P. Muggli, A. Scott, and R. Yoder
M. C. Thompson et al., Phys. Rev. Lett. 100, 214801 (2008).
Abstract: First measurements of the breakdown threshold in a dielectric subjected to GV/m wakefields produced by short (30–330 fs), 28.5 GeV electron bunches
have been made. Fused silica tubes of 100 µm inner diameter were exposed to a range of bunch lengths,
allowing surface dielectric fields up to 27 GV/m to be generated. The onset of breakdown, detected through
light emission from the tube ends, is observed to occur when the peak electric field at the dielectric
surface reaches 13.8±0.7 GV/m. The correlation of structure damage to beam-induced breakdown is
established using an array of postexposure inspection techniques. |
|
2008
|
High-Gradient Plasma Wakefield Acceleration with Two Subpicosecond Electron Bunches
E. Kallos, T. Katsouleas, W.D. Kimura, K. Kusche, P. Muggli, I. Pavlishin, I. Pogorelsky, D. Stolyarov, V. Yakimenko
E. Kallos et al., Phys. Rev. Lett. 100, 074802 (2008).
Abstract: A plasma wakefield experiment is presented where two 60-MeV
subpicosecond electron bunches are sent into a plasma produced by a capillary discharge.
Both bunches are shorter than the plasma wavelength, and the phase of the second bunch
relative to the plasma wave is adjusted by tuning the plasma density. It is shown that
the second bunch experiences a 150 MeV/m loaded accelerating gradient in the wakefield driven by the first bunch.
This is the first experiment to directly demonstrate high-gradient,
controlled acceleration of a short-pulse trailing electron bunch in a high-density plasma. |
|
2007
|
Hosing Instability in the Blow-Out Regime for Plasma-Wakefield Acceleration
C. Huang, W. Lu, M. Zhou, C.E. Clayton, C. Joshi, W.B. Mori, P. Muggli, S. Deng, E. Oz, T. Katsouleas, M.J. Hogan, I. Blumenfeld, F.J. Decker, R. Ischebeck, R.H. Iverson, N. A. Kirby, and D. Walz
C. Huang et al., Phys. Rev. Lett. 99, 255001 (2007).
Abstract: The electron hosing instability in the blow-out regime of plasma-wakefield acceleration is investigated using a linear perturbation theory about the electron blow-out
trajectory in Lu et al. [in Phys. Rev. Lett. 96, 165002 (2006)]. The growth of the instability is found to be affected by the beam parameters unlike in the standard theory Whittum et al. [Phys. Rev. Lett. 67, 991 (1991)] which is strictly valid for preformed channels.
Particle-in-cell simulations agree with this new theory, which predicts less hosing growth than found by the hosing theory of Whittum et al. |
|
2007
|
Ionization-induced electron trapping in ultrarelativistic plasma wakes
E. Oz, S. Deng, T. Katsouleas, P. Muggli, C. D. Barnes, I. Blumenfeld, F. J. Decker, P. Emma, M. J. Hogan, R. Ischebeck, R. H. Iverson,
N. Kirby, P. Krejcik, C. O'Connell, R. H. Siemann, D. Walz, D. Auerbach, C. E. Clayton, C. Huang, D. K. Johnson, C. Joshi, W. Lu, K. A. Marsh,
W. B. Mori, and M. Zhou
E. Oz et al., Phys. Rev. Lett. 98, 084801 (2007).
Abstract: The onset of trapping of electrons born inside a
highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions of a Li plasma confined by He gas. Li plasma electrons
support the wake, and higher ionization potential He atoms are ionized as the beam is focused by Li ions and can be trapped. As the wake amplitude is increased,
the onset of trapping is observed. Some electrons gain up to 7.6 GeV in a 30.5 cm plasma. The experimentally inferred trapping threshold is at a wake amplitude of
36 GV/m, in good agreement with an analytical model and PIC simulations. |
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2007
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Energy doubling of 42 GeV electrons in a metre-scale plasma wakefield accelerator
Ian Blumenfeld , Christopher E. Clayton, Franz-Josef Decker, Mark J. Hogan, Chengkun Huang, Rasmus Ischebeck , Richard Iverson, Chandrashekhar Joshi, Thomas Katsouleas, Neil Kirby, Wei Lu, Kenneth A. Marsh , Warren B. Mori, Patric Muggli, Erdem Oz, Robert H. Siemann, Dieter Walz, Miaomiao Zhou
I. Blumenfeld et al., Nature 445, 741-744 (15 February 2007).
Abstract: The energy frontier
of particle physics is several trillion electron volts, but colliders capable of reaching this regime (such as the Large Hadron Collider and
the International Linear Collider) are costly and time-consuming to build; it is therefore important to explore new methods of accelerating
particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields
that are orders of magnitude larger than those used in conventional colliders.In these accelerators, a drive beam (either laser or particle)
produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on
sustaining ultrahigh accelerating fields over a substantial length to achieve a significant energy gain. Here we show that an energy gain
of more than 42 GeV is achieved in a plasma wakefield accelerator of 85 cm length, driven by a 42 GeV electron beam at the Stanford Linear
Accelerator Center (SLAC). The results are in excellent agreement with the predictions of three-dimensional particle-in-cell simulations.
Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a
field of 52 GVm. This effectively doubles their energy, producing the energy gain of the 3-km-long SLAC accelerator in less than a metre
for a small fraction of the electrons in the injected bunch. This is an important step towards demonstrating the viability of plasma
accelerators for high-energy physics applications. |
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2006
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Positron Production by X Rays Emitted by Betatron Motion in a Plasma Wiggler
D. K. Johnson, D. Auerbach, I. Blumenfeld, C. D. Barnes, C. E. Clayton, F. J. Decker, S. Deng, P. Emma, M. J. Hogan, C. Huang, R. Ischebeck, R. Iverson, C. Joshi, T. C. Katsouleas, N. Kirby, P. Krejcik, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, C. L. O’Connell, E. Oz, R. H. Siemann, D. Walz, M. Zhou
D. K. Johnson et al., Phys. Rev. Lett. 97, 175003 (2006).
Abstract: Positrons in the energy
range of 3 to 30 MeV, produced by x rays emitted by betatron motion in a plasma wiggler of 28.5 GeV electrons from the SLAC accelerator,
have been measured. The extremely high-strength plasma wiggler is an ion column induced by the electron beam as it propagates through
and ionizes dense lithium vapor. X rays in the range of 1 to 50 MeV in a forward cone angle of 0.1 mrad collide with a 1.7 mm thick
tungsten target to produce electron-positron pairs. The positron spectra are found to be strongly influenced by the plasma
density and length as well as the electron bunch length. By characterizing the beam propagation in the ion column these
influences are quantified and result in excellent agreement between the measured and calculated positron spectra. |
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2006
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Plasma Production via Field Ionization
C. L. O’Connell, C. D. Barnes, F.-J. Decker, M. J. Hogan, R. Iverson, P. Krejcik, R. Siemann, D. R. Walz, C. E. Clayton, C. Huang, D. K. Johnson, C. Joshi, W. Lu, K. A. Marsh, W. Mori, M. Zhou, S. Deng, T. Katsouleas, P. Muggli, E. Oz
C. L. O’Connell et al., Phys. Rev. ST Accel. Beams 9, 101301 (2006).
Abstract: Plasma production via field ionization occurs when an incoming particle beam is sufficiently
dense that the electric field associated with the beam ionizes a neutral vapor or gas. Experiments conducted at the Stanford Linear Accelerator
Center explore the threshold conditions necessary to induce field ionization by an electron beam in a neutral lithium vapor. By independently
varying the transverse beam size, number of electrons per bunch, or bunch length, the radial component of the electric field is controlled to be
above or below the threshold for field ionization. Additional experiments ionized neutral xenon and neutral nitric oxide by varying the incoming beam?s bunch length.
A self-ionized plasma is an essential step for the viability of plasma-based accelerators for future high-energy experiments. |
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2006
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Hose Instability and Wake Generation by an Intense Electron Beam in a Self-Ionized Gas
S. Deng, C. D. Barnes, C. E. Clayton, C. O'Connell, F. J. Decker, R. A. Fonseca, C. Huang, M. J. Hogan, R. Iverson, D. K. Johnson, C. Joshi, T. Katsouleas, P. Krejcik, W. Lu, W. B. Mori, P. Muggli, E. Oz, F. Tsung, D. Walz, M. Zhou
S. Deng et al., Phys. Rev. Lett. 96, 045001 (2006).
Abstract: The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically
and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending
on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested. |
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2005
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Multi-GeV Energy Gain in a Plasma-Wakefield Accelerator
M. J. Hogan, C. D. Barnes, C. E. Clayton, F. J. Decker, S. Deng, P. Emma, C. Huang, R. H. Iverson, D. K. Johnson, C. Joshi, T. Katsouleas, P. Krejcik, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, C. L. O'Connell, E. Oz, R. H. Siemann, and D. Walz
M. J. Hogan et al., Phys. Rev. Lett. 95, 054802 (2005).
Abstract: A plasma-wakefield accelerator has accelerated particles by over 2.7 GeV
in a 10 cm long plasma module. A 28.5 GeV electron beam with 1.8x1010 electrons is compressed to 20 µm
longitudinally and focused to a transverse spot size of 10 µm at the entrance of a 10 cm long column of lithium
vapor with density 2.8x1017 atoms/cm3. The electron bunch fully ionizes the lithium vapor to
create a plasma and then expels the plasma electrons. These electrons return one-half plasma period later driving
a large amplitude plasma wake that in turn accelerates particles in the back of the bunch by more than 2.7 GeV.
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2004
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Possibility of a multibunch plasma afterburner for linear colliders
R. Maeda, T. Katsouleas, P. Muggli, C. Joshi, W. B. Mori, and W. Quillinan
R. Maeda et al., Phys. Rev. ST Accel. Beams 7, 111301 (2004).
Abstract: A concept for increasing the energy of a multibunch linear collider
using plasma wakefields is examined. The realization of high beam quality and high efficiency (and high luminosity)
requires more complexity than the original plasma afterburner concept proposed for doubling the energy of single
bunch linear colliders. This paper discusses the possibilities of using alternate bunches in the train to drive the
wake and accelerate upon it or alternately a few bunches to excite the wake and a single bunch to accelerate it.
Simulation results indicate that an energy of collision/energy of linac ratio of 2.8 can be obtained with 4% energy
spread and 0.29 relative luminosity by utilizing five drive bunches per accelerated bunch. The concept including
transverse effects is modeled with 2D linear plasma wakefield theory. |
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2004
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Meter-Scale Plasma-Wakefield Accelerator Driven by a Matched Electron Beam
P. Muggli, B. E. Blue, C. E. Clayton, S. Deng, F.-J. Decker, M. J. Hogan, C. Huang, R. Iverson, C. Joshi, T. C. Katsouleas, S. Lee, W. Lu, K. A. Marsh, W. B. Mori, C. L. O'Connell, P. Raimondi, R. Siemann, and D. Walz
P. Muggli et al., Phys. Rev. Lett. 93, 014802 (2004).
Abstract: A high-gradient, meter-scale plasma-wakefield accelerator module
operating in the electron blowout regime is demonstrated experimentally. The beam and plasma parameters are
chosen such that the matched beam channels through the plasma over more than 12 beam beta functions without
spreading or oscillating over a range of densities optimum for observing both deceleration and acceleration.
The wakefield decelerates the bulk of the initially 28.5 GeV beam by up to 155 MeV; however,
particles in the back of the same beam are accelerated by up to 280 MeV at a density of
1.9x10 14 cm -3 as the wakefield changes sign.
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2003
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Plasma Wakefield Acceleration in Self-ionized Gas or Plasmas
S. Deng, C. D. Barnes, C. E. Clayton, C. O'Connell, F. J. Decker, O. Erdem, R. A. Fonseca, C. Huang, M. J. Hogan, R. Iverson, D. K. Johnson, C. Joshi, T. Katsouleas, P. Krejcik, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, and F. Tsung
S. Deng et al., Phys. Rev. E68, 047401 (2003).
Abstract: Tunnel ionizing neutral gas with the self-field of a charged particle beam is explored as a possible way of creating plasma sources for a plasma wakefield accelerator
[Bruhwiler et al., Phys. Plasmas (to be published)]. The optimal gas density for maximizing the plasma wakefield without preionized plasma is studied using the PIC simulation code OSIRIS [R. Hemker et al.,
in Proceeding of the Fifth IEEE Particle Accelerator Conference (IEEE, 1999), pp. 3672?3674]. To obtain wakefields comparable to the optimal preionized case, the gas density needs to be seven times higher than the
plasma density in a typical preionized case. A physical explanation is given.
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2003
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Plasma-Wakefield Acceleration of an Intense Positron Beam
B. E. Blue, C. E. Clayton, C. L. O'Connell, F.-J. Decker, M. J. Hogan, C. Huang, R. Iverson, C. Joshi, T. C. Katsouleas, W. Lu, K. A. Marsh, W. B. Mori, P. Muggli, R. Siemann, and D. Walz
B.E. Blue et al., Phys. Rev. Lett. 90, 214801 (2003).
Abstract: Plasma wakefields are both excited and probed by propagating an intense 28.5GeV positron beam through a 1.4m long lithium plasma. The main body of the beam loses energy
in exciting this wakefield while positrons in the back of the same beam can be accelerated by the same wakefield as it changes sign. The scaling of energy loss with plasma density as well as the energy gain seen at
the highest plasma density is in excellent agreement with simulations.
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2003
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Ultrarelativistic Positron Beam Transport through Meter-scale Plasmas
M. J. Hogan, C. E. Clayton, C. Huang, P. Muggli, S. Wang, B. E. Blue, D. Walz, K. A. Marsh, C. L. O'Connell, S. Lee, R. Iverson, F.-J. Decker, P. Raimondi, W. B. Mori, T. C. Katsouleas, C. Joshi, and R. H. Siemann
M. J. Hogan et al., Phys. Rev. Lett. 90, 205002 (2003).
Abstract:
We report on the first study of the dynamic transverse forces imparted to an ultrarelativistic positron beam by a long plasma in the underdense regime. Focusing of the 28.5 GeV beam is observed from time-resolved beam profiles after
the 1.4 m plasma. The strength of the imparted force varies along the ~12 ps full length of the bunch as well as with plasma density. Computer simulations substantiate the longitudinal aberration seen in the data and reveal mechanisms
for emittance degradation.A physical explanation is given.
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2002
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Dynamic Focusing of an Electron Beam through a Long Plasma
C. O'Connell, F-J. Decker, M. J. Hogan, R. Iverson, P. Raimondi, R. H. Siemann, D. Walz, B. Blue, C. E. Clayton, C. Joshi, K. A. Marsh, W. B. Mori, S. Wang, T. Katsouleas, S. Lee, and P. Muggli
C. O'Connell et al., Phys. Rev. ST Accel. Beams 5, 121301 (2002).
Abstract: The focusing effects of a 1.4 m long, (0–2)x1014 cm-3 plasma on a single 28.5 GeV electron bunch are studied experimentally in the underdense
or blowout regime, where the beam density is much greater than the plasma density. As the beam propagates through the plasma, the density of plasma electrons along the incoming bunch drops from the ambient density to zero leaving
a pure ion channel for the bulk of the beam. Thus, from the head of the beam up to the point where all plasma electrons are blown out, each successive longitudinal slice of the bunch experiences a different focusing force due to
the plasma ions. The time-changing focusing force results in a different number of betatron oscillations for each slice depending upon its location within the bunch. By using an electron beam that has a correlated energy spread,
this time-dependent focusing of the electron bunch has been observed by measuring the beam spot size in the image plane of a magnetic energy spectrometer placed at the plasma exit.
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2002
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High energy density plasma science with an ultrarelativistic electron beam
C. Joshi, B. Blue, C. E. Clayton, E. Dodd, C. Huang, K. A. Marsh, W. B. Mori, S. Wang, M. J. Hogan, C. O'Connell, R. Siemann, D. Watz, P. Muggli, T. Katsouleas, S. Lee
C. Joshi et al., Phys. Plasmas 9, 1845 (2002).
Abstract: An intense, high-energy electron or positron beam can have focused intensities rivaling those of
today's most powerful laser beams. For example, the 5 ps (full-width, half-maximum), 50 GeV
beam at the Stanford Linear Accelerator Center (SLAC) at 1 kA and focused to a 3 micron rms spot
size gives intensities of 1020 W/cm2 at a repetition rate of .10 Hz. Unlike a ps or fs laser pulse
which interacts with the surface of a solid target, the particle beam can readily tunnel through tens
of cm of steel. However, the same particle beam can be manipulated quite effectively by a plasma
that is a million times less dense than air! This is because of the incredibly strong collective fields
induced in the plasma by the Coulomb force of the beam. The collective fields in turn react back
onto the beam leading to many clearly observable phenomena. The beam paraticles can be: (1)
Deflected leading to focusing, defocusing, or even steering of the beam; (2) undulated causing the
emission of spontaneous betatron x-ray radiation and; (3) accelerated or decelerated by the plasma
fields. Using the 28.5 GeV electron beam from the SLAC linac a series of experiments have been
carried out that demonstrate clearly many of the above mentioned effects. The results can be
compared with theoretical predictions and with two-dimensional and three-dimensional, one-to-one,
particle-in-cell code simulations. These phenomena may have practical applications in future
technologies including optical elements in particle beam lines, synchrotron light sources, and
ultrahigh gradient accelerators.
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2002
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Transverse Envelope Dynamics of a 28.5-GeV Electron Beam in a Long Plasma
C. E. Clayton, B. E. Blue, E. S. Dodd, C. Joshi, K. A. Marsh, W. B. Mori, S. Wang, P. Catravas, S. Chattopadhyay, E. Esarey, W. P. Leemans, R. Assmann, F. J. Decker, M. J. Hogan, R. Iverson, P. Raimondi, R. H. Siemann, D. Walz, T. Katsouleas, S. Lee, and P. Muggli
C. E Clayton et al., Phys. Rev. Lett. 88, 154801 (2002).
Abstract:
The transverse dynamics of a 28.5-GeV electron beam propagating in a 1.4 m long, (0–2) x 1014 cm-3 plasma are studied experimentally in the underdense or blowout regime.
The transverse component of the wake field excited by the short electron bunch focuses the bunch, which experiences multiple betatron oscillations as the plasma density is increased. The spot-size
variations are observed using optical transition radiation and Cherenkov radiation. In this regime, the behavior of the spot size as a function of the plasma density is well described by a simple
beam-envelope model. Dynamic changes of the beam envelope are observed by time resolving the Cherenkov light.
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2002
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X-Ray Emission from Betatron Motion in a Plasma Wiggler
S. Wang, C. E. Clayton, B. E. Blue, E. S. Dodd, K. A. Marsh, W. B. Mori, C. Joshi, S. Lee, P. Muggli, T. Katsouleas, F. J. Decker, M. J. Hogan, R. H. Iverson, P. Raimondi, D. Walz, R. Siemann, and R. Assmann
S. Wang et al., Phys. Rev. Lett. 88, 135004 (2002).
Abstract: The successful utilization of an ion channel in a plasma to wiggle a 28.5-GeV
electron beam to obtain broadband x-ray radiation is reported. The ion channel is induced by the electron bunch as it propagates through an underdense 1.4-meter-long lithium plasma. The quadratic density
dependence of the spontaneously emitted betatron x-ray radiation and the divergence angle of ~(1–3)x1014 radian of the forward-emitted x-rays as a consequence of betatron motion in the ion
channel are in good agreement with theory. The absolute photon yield and the peak spectral brightness at 14.2-keV photon energy are estimated.
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2002
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Energy Doubler for a Linear Collider
S. Lee, T. Katsouleas, P. Muggli, W. B. Mori, C. Joshi, R. Hemker, E. S. Dodd, C. E. Clayton, K. A. Marsh, B. Blue, S. Wang, R. Assmann, F. J. Decker, M. Hogan, R. Iverson, and D. Walz
S. Lee et al., Phys. Rev. ST Accel. Beams 5, 121301 (2002).
Abstract: The concept of using short plasma sections several meters in length to double the energy of a linear collider just before the collision point is proposed and modeled.
In this scenario the beams from each side of a linear collider are split into pairs of microbunches with the first driving a plasma wake that accelerates the second. The luminosity of the doubled collider is maintained by
employing plasma lenses to reduce the spot size before collision.
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2001
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Measurements of Radiation near an Atomic Spectral Line from the Interaction of a 30 GeV Electron Beam and a Long Plasma
P. Catravas, S. Chattopadhyay, E. Esarey, W. P. Leemans, R. Assmann, F.-J. Decker, M. J. Hogan, R. Iverson, R. H. Siemann, D. Walz, D. Whittum, B. Blue, C. Clayton, C. Joshi, K. A. Marsh, W. B. Mori, S. Wang, T. Katsouleas, S. Lee, and P. Muggli
P. Catravas et al., Phys. Rev. E 64, 046502 (2001).
Abstract: Emissions produced or initiated by a 30-GeV electron beam propagating through a ~1-m long heat pipe oven containing neutral and partially ionized vapor
have been measured near atomic spectral lines in a beam-plasma wakefield experiment. The Cerenkov spatial profile has been studied as a function of oven temperature and pressure, observation wavelength,
and ionizing laser intensity and delay. The Cerenkov peak angle is affected by the creation of plasma, and estimates of neutral and plasma density have been extracted. Increases in visible background radiation,
consistent with increased plasma recombination emissions due to dissipation of wakefields, were simultaneously measured.
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2001
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Collective Refraction of a Beam of Electrons at a Plasma-gas Interface
P. Muggli, S. Lee, T. Katsouleas, R. Assmann, F. J. Decker, M. J. Hogan, R. Iverson, P. Raimondi, R. H. Siemann, D. Walz, B. Blue, C. E. Clayton, E. Dodd, R. A. Fonseca, R. Hemker, C. Joshi, K. A. Marsh, W. B. Mori, and S. Wang
P. Muggli et al., Phys. Rev. ST Accel. Beams 4, 091301 (2001).
Abstract: In a recent Brief Comment, the results of an experiment to measure the refraction of a particle beam were reported [P. Muggli et al., Nature 411, 43 (2001)].
The refraction takes place at a passive interface between a plasma and a gas. Here the full paper on which that Comment is based is presented. A theoretical model extends the results presented previously
[T. Katsouleas et al., Nucl. Instrum. Methods Phys. Res., Sect. A 455, 161 (2000)]. The effective Snell's law is shown to be nonlinear, and the transients at the head of the beam are described.
3D particle-in-cell simulations are performed for parameters corresponding to the experiment. Additionally, the experiment to measure the refraction and internal reflection at the Stanford Linear Accelerator Center is described.
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2001
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Boundary effects: Refraction of a particle beam
Patric Muggli, Seung Lee, Thomas Katsouleas, Ralph Assmann, Franz-Joseph Decker, Mark J. Hogan, Richard Iverson, Pantaleo Raimondi, Robert H. Siemann, Dieter Walz, Brent Blue, Christopher E. Clayton, Evan Dodd, Ricardo Fonseca, Roy Hemker, Chandrashekhar Joshi, Kenneth A. Marsh, Warren B. Mori, Shoquin Wang
P. Muggli et al., Nature 411, 43-43 (03 May 2001).
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2001
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Simulations of Cerenkov wake radiation sources
N. Spence, T. Katsouleas, P. Muggli, W. B. Mori, and R. Hemker
N. Spence et al., Phys. Plasmas 8, 4995 (2001).
Abstract: The Cerenkov wakes stimulated by various drivers (an intense laser pulse, a train of laser pulses or
beats and a relativistic particle bunch) propagating transverse to a dc magnetic field in a plasma are
analyzed. In each case, the wake generated couples to the electromagnetic radiation of approximate
frequency ωp at the plasma-vacuum boundary. The radiation amplitude is Ωc/ωp times the
amplitude of the wake excited in the plasma (for a sharp boundary). Two- and three-dimensional
particle-in-cell simulations are used to verify the scaling laws. For the parameters of current plasma
wake field accelerator experiments the results predict that generation of high-power ~GW coherent
microwave to terahertz radiation is possible.
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2001
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High power radiation from ionization fronts in a static electric field in a waveguide
J. R. Hoffman, P. Muggli, R. Liou, M. Gundersen, J. Yampolsky, T. Katsouleas, C. Joshi, and W. B. Mori
J. R. Hoffman et al., J. Appl. Phys. 90, 1115 (2001).
Abstract: The radiation produced when a relativistically moving plasma/gas boundary (i.e., an ionization
front) passes between alternatively biased capacitor electrodes is studied. Results of an experiment
based on a design which incorporates the capacitor electrodes into an X band waveguide are
presented. The waveguided design effectively couples nearly three orders of magnitude more power
into the output than the previously unguided designs. Linear theory is extended to include the
depletion of the laser energy as it propagates through the ionizable gas (i.e., laser depletion), and the
effect of finite output pulse duration.
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2000
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E-157: A 1.4-m-long plasma wake field acceleration experiment using a 30 GeV electron beam from the Stanford Linear Accelerator Center Linac
M.J. Hogan, R. Assmann, F.-J. Decker, R. Iverson, P. Raimondi, S. Rokni, R.H. Siemann, D. Walz, D. Whittum, B. Blue, C.E. Clayton, E. Dodd, R. Hemker, C. Joshi, K.A. Marsh, W. B. Mori, S. Wang, T. Katsouleas, S. Lee, P. Muggli, P. Catravas, S. Chattopadhyay, E. Esarey, W.P. Leemans
M. J. Hogan et al., Phys. Plasmas 7, 2241 (2000).
Abstract: In the E-157 experiment now being conducted at the Stanford Linear Accelerator Center, a 30GeV
electron beam of 2×1010 electrons in a 0.65-mm-long bunch is propagated through a 1.4-m-long
lithium plasma of density up to 2×1014 e-/cm3. The initial beam density is greater than the plasma
density, and the head of the bunch expels the plasma electrons leaving behind a uniform ion channel
with transverse focusing fields of up to several thousand tesla per meter. The initial transverse beam
size with σ=550?100 µm is larger than the matched size of 5 µm resulting in up to three beam
envelope oscillations within the plasma. Time integrated optical transition radiation is used to study
the transverse beam profile immediately before and after the plasma and to characterize the
transverse beam dynamics as a function of plasma density. The head of the bunch deposits energy
into plasma wakes, resulting in longitudinal accelerating fields which are witnessed by the tail of the
same bunch. A time-resolved Cherenkov imaging system is located in an energy dispersive plane
downstream of the plasma. It images the beam onto a streak camera allowing time-resolved
measurements of the beam energy spectrum as a function of plasma density. Preliminary
experimental data from the first three runs are compared to theory and computer simulations.
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2000
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Guest Editorial, Special Issue on Laser and Plasma Accelerators, IEEE Transactions on Plasma Science
P. Muggli and T.M. Antonsen, Jr.
P. Muggli and T.M. Antonsen, Jr.,IEEE Trans. On Plasma Sci., 28(4), p. 1054 (2000).
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2000
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Investigation of a channeling high intensity laser-beam in underdense plasmas
Z. Najmudin, A.E. Dangor, A. Modena, C.E. Clayton, D. Gordon, C. Joshi, K.A. Marsh, P. Muggli, V. Malka, C. Danson, D. Neely, and F.N. Walsh
Z. Najmudin et al., IEEE Trans. On Plasma Sci., 28(4), p. 1057 (2000).
Abstract: The interaction of an intense short pulse laser (5×10 18 W/cm 2) with underdense plasma was extensively studied.
The beam is found to be highly susceptible to the forward Raman
scattering instability. At sufficiently high growth rates, this can
lead to wavebreaking with the resultant production of a high flux
of accelerated electrons (10 11 for E=2 MeV). Some electrons
are found to be accelerated well above the dephasing energy, up to
94 MeV. Self-scattered images intimate the presence of high-intensity
channels that extend more than 3.5mm or 12 Rayleigh lengths.
These filaments do not follow the axis of laser propagation, but are
seen to be emitted within an 4 cone centered around this axis.
Spectra of the self-scattered light show that the main contribution
of the scattering is not from light captured within these filaments.
But there is evidence for self-phase modulation from effects
such as ionization and relativistic self-focusing. However, no clear
correlation is observed between channel length and the number
or energies of accelerated electrons. Evidence for high intensities
within the channels is given by small-angle Thomson scattering of
the plasma wave generated therein. With this method, the intensity
is found to be of the order of 10 18 W/cm 2 greater than 12
Rayleigh lengths from focus.
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2000
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Plasma Source Test and Simulation Results for the Underdense Plasma Lens Experiment at the UCLA Neptune Laboratory
H. Suk, C. E. Clayton, C. Joshi, T.C. Katsouleas, P. Muggli, R. Narang, C. Pellegrini, J.B. Rosenzweig
H. Suk et al., IEEE Transactions on Plasma Science, vol.28, no.1, pp.271-7 (2000).
Abstract: The planned plasma lens experiment at the UCLA
Neptune Laboratory is described. In the experiment, electron
beams with an energy of 16 MeV, a charge of 4 nC, and a
pulse duration of 30 ps [full-width at half-maximum (FWHM)]
are designed to be produced from the 1.625-cell photoinjector
radio-frequency gun (=2.856 GHz) and PWT linac in
the Neptune. The generated beams are passed through a thin
underdense argon plasma with a density of low 1012 cm-3 range
and a thickness of a few centimeters. For this experiment, a
LaB6-based discharge plasma source was developed and tested. In
this paper, the overview of the planned plasma lens experiment
and the test results of the plasma source for various conditions
are presented. In addition, computer simulations with a 2-1/2
dimensional particle-in-cell code (MAGIC) were performed and
the simulation results are shown.
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1999
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1999
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Homogeneous meter-long plasma source for advanced accelerator applications
P. Muggli, K.A. Marsh, S. Wang, C.E. Clayton, S. Lee, T.C. Katsouleas, and C. Joshi
P. Muggli et al., IEEE Trans. on Plasma Science 27(3), pp. 791-799 (1999).
Abstract: A photo-ionized lithium source is developed for
plasma acceleration applications. A homogeneous column of
lithium neutral vapor with a density of 2×10 15 cm -3 is confined
by helium gas in a heat-pipe oven. A UV laser pulse ionizes the
vapor. In this device, the length of the neutral vapor and plasma
column is 25 cm. The plasma density was measured by laser
interferometry in the visible on the lithium neutrals and by CO 2
laser interferometry on the plasma electrons. The maximum
measured plasma density was 2.9×10 14 cm -3, limited by
the available UV fluence (83 mJ/cm 2), corresponding to a
15% ionization fraction. After ionization, the plasma density
decreases by a factor of two in about 12 µs. These results show
that such a plasma source is scaleable to lengths of the order of
1 m and should satisfy all the requirements for demonstrating
the acceleration of electrons by 1 GeV in a 1 GeV/m amplitude
plasma wake.
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1998
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The Neptune photoinjector
J. Rosenzweig, S. Anderson, K. Bishofberger, X. Ding, A. Murokh, C. Pellegrini, H. Suk, A. Tremaine, C.E. Clayton, C. Joshi, K.A. Marsh, P. Muggli
J. Rosenzweig et al., Nucl. Instr. Meth. Phys. Res. A 410, pp. 437-451 (1998).
Abstract: The RF photoinjector in the Neptune advanced accelerator laboratory, along with associated beam diagnostics, transport and phase-space manipulation techniques are described. This versatile injector has been designed to produce short-pulse electron beams for a variety of uses: ultra-short bunches for injection into a next-generation plasma beatwave acceleration experiment, space-charge dominated beam physics studies,
plasma wake-field acceleration driver, plasma lensing, and free-electron laser microbunching techniques.
The component parts of the photoinjector, the RF gun, photocathode drive laser systems, booster linac,
RF system, chicane compressor, beam diagnostic systems, and control system, are discussed. The present
status of photoinjector commissioning at Neptune is reviewed, and proposed experiments are detailed.
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1998
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Plasma Wave Generation in a Self-Focused Channel of a Relativistically Intense Laser Pulse
C. E. Clayton, K.-C. Tzeng, D. Gordon, P. Muggli, W. B. Mori, C. Joshi, V. Malka, Z. Najmudin, A. Modena, D. Neely, and A. E. Dangor
C. E. Clayton et al., Phys. Rev. Lett. 81, 100-103 (1998).
Abstract: Evidence for self-channeling of a relativistically intense laser pulse
in an underdense plasma is presented through Schlieren and 90° Thomson sidescatter images. Using collective Thomson
scattering of a probe beam, we observe that relativistically propagating plasma waves are excited over the entire length
of the channel, up to 12 Rayleigh lengths (~4 mm). From the wave amplitude, the intensity inside the channel is
estimated to be ~1018 W/cm2.
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1998
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Generation of microwave pulses from the static electric field of a capacitor array by an underdense, relativistic ionization front
P. Muggli, R. Liou, C. H. Lai, J. Hoffman, T. C. Katsouleas, and C. Joshi
P. Muggli et al., Phys. Plasmas 5, 2112 (1998).
Abstract: The dc to ac radiation converter is a new device in which a relativistic ionization front directly
converts the static electric field of an array of alternatively biased capacitors into a pulse of tunable
radiation. In a proof-of-principle experiment frequencies between 6 and 21 GHz were generated
with plasma densities in the 1012 cm-3 range and a capacitor period 2d=9.4 cm. In the present
experiment, short pulses with frequencies between 39 and 84 GHz are generated in a structure with
2d=2 cm. The frequency spectra of these pulses are measured using a diffraction grating. The
spectra are discrete, and their center frequency varies linearly with the gas pressure prior to
ionization (or plasma density), as expected from theory. Their relative spectral width is around 18%,
consistent with the expected number of cycles (six) contained in the pulses. An upper limit of 750
psec (bandwidth detection limited) is placed on the pulses length. The emitted frequency increases
from 53 to 93 GHz when the capacitors are connected by pair to obtain a effective array period of
4 cm.
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1998
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Observation of Electron Energies Beyond the Linear Dephasing Limit from a Laser-Excited Relativistic Plasma Wave
D. Gordon, K. C. Tzeng, C. E. Clayton, A. E. Dangor, V. Malka, K. A. Marsh, A. Modena, W. B. Mori, P. Muggli, Z. Najmudin, D. Neely, C. Danson, and C. Joshi
D. Gordon et al., Phys. Rev. Lett. 80, 2133-2136 (1998).
Abstract: The spatial extent of the plasma wave and the spectrum of
the accelerated electrons are simultaneously measured when the relativistic plasma wave associated with Raman
forward scattering of an intense laser beam reaches the wave breaking limit. The maximum observed energy of 94 MeV
is greater than that expected from the phase slippage between the electrons and the accelerating electric field as
given by the linear theory for preinjected electrons. The results are in good agreement with 2D particle-in-cell
code simulations of the experiment.
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1998
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Generation of ultrashort, discrete spectrum microwave pulses using the dc to ac radiation converter
P. Muggli, R. Liou, J. Hoffman, T. Katsouleas, and C. Joshi
P. Muggli et al., Appl. Phys. Lett. 72, 19 (1998).
Abstract: The output radiation of a dc to ac radiation converter is characterized. A relativistic ionization front
passing through a capacitor array of period d=1cm produces short pulses of tunable radiation
between 39 and 84 GHz with a gas pressure between 0 and 30 mT. The frequency spectra of the
produced pulses are discrete and exhibit full widths at half maximum between 12% and 28%,
consistent with the expected width for six cycles? pulses. An upper bound of 750 ps (detection
bandwidth limited) is placed on the pulse widths. These are the shortest pulses produced by a source
of coherent radiation in this frequency range.
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1996
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1996
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Demonstration of Microwave Generation from a Static Field by a Relativistic Ionization Front in a Capacitor Array
C. H. Lai, R. Liou, T. C. Katsouleas, P. Muggli, R. Brogle, C. Joshi, and W. B. Mori
C. H. Lai et al., Phys. Rev. Lett. 77, 4764-4767 (1996).
Abstract: We present the results of a proof-of-principle experiment to demonstrate the generation of tunable radiation from a laser-ionized gas-filled capacitor array. This scheme directly converts a static electric field of wave number k 0 into coherent radiation pulses of frequency ω p2/2k 0c, where ω p is the plasma frequency. The radiation frequency can be tuned by varying gas pressure and/or capacitor spacing. In this experiment, well-polarized, short (less than 5 ns) microwave pulses have been generated over a frequency range of 6 to 21 GHz. The frequency of the detected signal, as measured with cut-off waveguides, scales linearly with the plasma density, and the relative power of the signal scales quadratically with the dc bias voltage in agreement with the theory.
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1996
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Photoemission from diamond and fullerene films for advanced accelerator application
P. Muggli, R. Brogle, S. Jou, H.J. Doerr, R.F. Bunshah, and C. Joshi
P. Muggli et al., IEEE Trans. on Plasma Science 24(2), 428 (1996).
Abstract: The photoemission properties of thin diamond and
fullerene films were investigated for advanced accelerator applications,
using subpicosecond laser pulses at three different
wavelengths (650, 325, and 217 nm). The quantum efficiency
(QE) obtained at 217 nm with a boron-doped, p-type, (111)
polycrystalline diamond film (2.6×l0-4) was only five times
smaller than the QE obtained with a mirror polished copper
sample (1.3×10-3) but more than nine times larger than the
QE obtained with a pure diamond film or with natural diamond
monocrystals. Similar results were obtained for the two-photon
electron yields at 325 nm. The electron yields obtained with pure
fullerene films were small and comparable to the ones observed
with the pure diamond samples. With 650 nm pulses, the damage
threshold of the (110) Type IIa natural diamond monocrystal
(9.38×l04 µJ cm-2), defined here as the fluence leading to
an onset of ion emission, was 25 times larger than the damage
threshold for a copper sample (3.75×l03 µJ cm-2). The damage
threshold of the boron-doped sample at the same wavelength was
two times larger than that of copper. Damage thresholds with 325
nm pulses were lower, and with 217 nm pulses ion emission was
observed at all fluences probably attributed to ablation of surface
hydrocarbon contaminants. Results show that high-quality highboron
concentration diamond films could be a good candidate
for high-RF electron guns.
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1995
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1995
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Two-color photoemission produced by femtosecond laser pulses on copper
P. Muggli, R. Brogle, C. Joshi
P. Muggli et al., JOSA B, Vol. 12, Issue 4, pp. 553 (April 1995).
Abstract: Single-color illumination of a copper surface by a red or an ultraviolet femtosecond laser pulse yields a threephoton
(red) or a two-photon (UV) photoemission process. A multicolor, multiphoton process is generated
when the red and the UV pulses overlap both in space and in time on the photocathode. It is shown that
this emission process results from the absorption by an electron of one red and one UV photon. It provides
a means to correlate ultrashort laser pulses of different wavelengths.
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1993
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High power gyrotrons at 8 GHz : 8 GHz gyrotron development at the Centre de Recherches en Physique des Plasmas, Lausanne
P. Muggli and M.Q. Tran, in "Gyrotron Oscillators, their Principles and Practice," C.J. Edgcombe editor, published by Taylor and Francis, pp. 295-303, (1993).
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1992
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Parasitic Oscillation in and Suppression of a Gyrotron Backward Wave Mode in a Low-Q 8 GHz Gyrotron
P. Muggli, M. Q. Tran, and T. M. Tran
P. Muggli et al., IEEE TRANSACTIONS ON PLASMA SCIENCE. VOL. 20, NO. 4, AUGUST (1992).
Abstract: The parasitic oscillation of the TEo02 gyrotron backward
wave (gyro BW) mode is observed in a low-Q, 8 GHz TEo011,
gyrotron. Although at low power (PBW < 5 kW), the oscillation
of the gyro BW mode, simultaneously with the gyrotron mode,
results in a maximum TEo012 mode efficiency of less than 0.25. The
parasitic oscillation is suppressed by operating the gyrotron with
a negative magnetic field gradient along the electron beam, which
allows the maximum efficiency to reach 0.40 and the output power
to be multiplied by a factor varying from 1.4 to 1.7. The optimum
efficiency curve of the TEo011 mode indicates that the low-Q
cavity behaves as a much higher Qdiff cavity. Excessive values
of magnetic field gradient and alpha favor the TEo012 longitudinal
mode, which oscillates in place of the TEo011 mode and limits its
maximum output power. This competitive process is responsible
for the high-Q-like behavior of the optimum efficiency curve.
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1991
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1991
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Velocity ratio measurement using the frequency of the gyro-backward wave
P. Muggli, M.Q. Tran and T.M. Tran
P. Muggli et al., Physics of Fluids B-3(6), pp. 1315-1318, (1991).
Abstract: The operating diagram of a low quality factor, 8 GHz TEo01 gyrotron exhibits oscillations
between 6.8 and 7.3 GHz. These oscillations are identified as the backward wave component of
the TEo21 traveling mode. As the resonance condition of this mode depends on the
average parallel velocity (vpar) of the beam electrons (ωBw~Ωc/γ-kparvpar), the measurement
of ωBw for given Ωc, and γ is used as a diagnostic for the beam electrons velocity ratio
α=vperp/vpar. The values of α, deduced from ωBw through the linear dispersion relation for
the electron cyclotron instability in an infinite waveguide, are unrealistic. A nonlinear
simulation code gives a values that are in very good agreement with the ones predicted by a
particle trajectory code (+10% to +20%). It is found numerically that the particles?
velocity dispersion in vpar and vperp increases ωBw. This effect explains part of the discrepancy
between the values of α inferred from ωBw without velocity dispersion and the expected
values.
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1990
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Experimental measurement of competition between fundamental and second harmonic emission in a quasi-optical gyrotron
S. Alberti, M. Pedrozzi, M.Q. Tran, J. P. Hogge, T.M. Tran, P. Muggli, B. Jodicke and H. G. Mathews
S. Alberti et al., Phys. Fluids B2(7) (Letters), pp. 2544-2546, (1990).
Abstract: A quasi-optical gyrotron (QOG) designed for operation at the fundamental (f ce=100GHz) exhibits simultaneous emission at fce and 2f ce (second harmonic).
For a beam current of 4 A, 20% of the total rf power is emitted at the second harmonic. The experimental measurements show that the excitation of the second harmonic is only possible when the fundamental is present. The frequency of the second harmonic is locked by the frequency of the fundamental.
Experimental evidence shows that when the second harmonic is not excited, total efficiency is enhanced.
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1990
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Effect of power reflection on the operation of a low-Q 8 GHz gyrotron
P. Muggli, M.Q. Tran, T.M. Tran, H.-G. Mathews, G. Agosti, S. Alberti and A. Perrenoud
P. Muggli et al., IEEE Transactions on Microwave Theory and Techniques, MTT-38(9), pp.1345-1351, (1990).
Abstract: The operating characteristics of a low-Q (Qcav=225),
8 GHz gyrotron oscillator operating in the TEo011 mode and submitted to
various mismatched loads are reported. Under matched conditions,
output power np to 310 kW (η=35%) and maximum efficiency up to
43% have been measured. In general, power reflection from loads with
different phases and amplitudes leads to an output power decrease.
Excessive reflections cause mode switching (TEo011 to TEo012) or even
arcing inside the tube. The effect of power reflection is seen to increase
rapidly with current and output power. Nevertheless, we have observed
that, as predicted by calculations, the maximum output power is not
reached under matched conditions but with a specific nonzero value of
the complex reflection coefficient.
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1990
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Experimental measurements on a 100 GHz frequency tunable quasi-optical gyrotron
S. Alberti, M.Q. Tran, J. P. Hogge, T.M. Tran, A. Bondeson, P. Muggli, A. Perrenoud, B. Jodicke and H. G. Mathews
S. Alberti et al., Phys. Fluids B2(7), pp. 1654-1661 (1990).
Abstract: Experiments on a 100 GHz quasioptical (QO) gyrotron operating at the fundamental
(ω=Ωce) are described. Powers larger than 90 kW at an efficiency of about 12% were achieved. Depending on the electron beam parameters, the frequency spectrum of the output can be either single moded or multimoded.
One of the main advantages of the QO gyrotron over the conventional gyrotron is its continuous frequency tunability. Various techniques to tune the output frequency have been tested, such as changing the mirror separation,
the beam voltage, or the main magnetic field. Within the limitations of the present setup, 5% tunability was achieved. The QO gyrotron designed for operation at the fundamental frequency exhibits simultaneous
emission at 100 GHz (fundamental) and 200 GHz (second harmonic). For a beam current of 4 A, 20% of the total rf power is emitted at the second harmonic.
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1989
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Prospects for high power, quasi-optical gyrotrons operating in the millimeter wave range
T.M. Tran, M.Q. Tran, S. Alberti, J. P. Hogge, B. Isaak, P. Muggli and A. Perrenoud
T.M. Tran et al., IEEE Trans. Elect. Device 36, pp. 1983-1990 (1989).
Abstract: The prospects for high-power (several megawatts) quasi-optical gyrotrons operating in
the high-frequency region (≥150 GHz) are considered. The analysis is mainly concerned with the physics of interaction between the annular electron beam and the electromagnetic field within the quasi-optical
resonator, together with the constraints required by long-pulse or CW operations. It is shown that powers of several megawatts at frequencies exceeding 150 GHz are possible if one can maintain single-mode
operation in the overmoded quasi-optical resonators. A thorough performance study of the magnetron injection gun for such high-power gyrotrons is carried out using the adiabatic theory as well as numerical
simulations
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1986
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