|
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2012
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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., accepted for publication in Phys. of Plasmas (April 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. |
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2011
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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. |
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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. |
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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. |
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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. |
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2010
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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. |
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2010
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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. |
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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. |
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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. |
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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 |
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2009
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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. |
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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. |
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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. |
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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. |
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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. |
|
2007
|
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. |
|
2006
|
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. |
|
2006
|
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. |
|
2006
|
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. |
|
2005
|
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
|
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 1.9x1014 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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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 (5×1018 W/cm2) 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 (1011 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 1018 W/cm2 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 2×1015 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 CO2
laser interferometry on the plasma electrons. The maximum
measured plasma density was 2.9×1014 cm-3, limited by
the available UV fluence (83 mJ/cm2), 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 k0 into coherent radiation pulses of frequency ωp2/2k0c, where ωp 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 (fce=100GHz) exhibits simultaneous emission at fce and 2fce (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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