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Lu, W.

Paper Title Page
THPMS023 Designing LWFA in the Blowout Regime 3050
 
  • W. Lu, C. Joshi, W. B. Mori, F. S. Tsung, M. Tzoufras
    UCLA, Los Angeles, California
  • S. Fonseca, L. O. Silva, J. H. Vieira
    Instituto Superior Tecnico, Lisbon
 
  Funding: This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345.

The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than that in current accelerators has been well documented. We develop a phenomenological framework for Laser Wakefield Acceleration (LWFA) in the 3D nonlinear regime, in which the plasma electrons are expelled by the radiation pressure of a short pulse laser, leading to nearly complete blowout. This theory provides a recipe for designing a LWFA for given laser and plasma parameters and estimates the number and the energy of the accelerated electrons whether self-injected or externally injected. These formulas apply for self-guided as well as externally guided pulses (e.g. by plasma channels). Based on this theory, we will present scenarios on how to build a single stage accelerator with output energies from GeV to TeV. Particle-In-Cell (PIC) simulations are used to verify our theory. This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345.

 
THPMS028 The Physical Picture of Beam Loading in the Blowout Regime 3061
 
  • M. Tzoufras, C. Huang, W. Lu, W. B. Mori, F. S. Tsung
    UCLA, Los Angeles, California
  • S. Fonseca, L. O. Silva, J. H. Vieira
    Instituto Superior Tecnico, Lisbon
 
  Funding: This work is supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345.

The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion of plasma electrons. Furthermore, the generation of a high quality electron beam requires proper loading of the wake. We have developed a theoretical framework which predicts the maximum number of electrons which can be loaded in the wake, as well as the optimal charge density profile for beam loading. Using the PIC codes OSIRIS and QuickPIC we present designs of LWFA accelerators that verify our theoretical estimates as well as demonstrate the potential of LWFA to produce high energy electron beams with high beam quality.

 
WEYKI01 Results of the Energy Doubler Experiment at SLAC 1910
 
  • M. J. Hogan, I. Blumenfeld, F.-J. Decker, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745. DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345.

The costs and the time scales of colliders intended to reach the energy frontier are such that it is 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 ultra-high accelerating fields over a substantial length to achieve a significant energy gain. More than 42 GeV energy gain was achieved in an 85 cm long plasma wakefield accelerator driven by a 42 GeV electron drive beam at the Stanford Linear Accelerator Center (SLAC). 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 GV/m. 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.

 
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THPMS029 Beam Head Erosion in Self-ionized Plasma Wakefield Accelerators 3064
 
  • M. Zhou, C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori
    UCLA, Los Angeles, California
  • M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  Funding: Work supported by Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345

In the recent plasma wakefield accelerator experiments at SLAC, the energy of the particles in the tail of the 42 GeV electron beam were doubled in less than one meter [1]. Simulations suggest that the acceleration length was limited by a new phenomenon – beam head erosion in self-ionized plasmas. In vacuum, a particle beam expands transversely in a distance given by beta*. In the blowout regime of a plasma wakefield [2], the majority of the beam is focused by the ion channel, while the beam head slowly spreads since it takes a finite time for the ion channel to form. It is observed that in self-ionized plasmas, the head spreading is exacerbated compared to that in pre-ionized plasmas, causing the ionization front to move backward (erode). A simple theoretical model is used to estimate the upper limit of the erosion rate for a bi-gaussian beam by assuming free expansion of the beam head before the ionization front. Comparison with simulations suggests that half this maximum value can serve as an estimate for the erosion rate. Critical parameters to the erosion rate are discussed.

[1] I. Blumenfeld et al., Nature 445, 741(2007)[2] J. B. Rosenzweig et al., Phys. Rev. A 44, R6189 (1991)

 
THPMS033 Scaling of Energy Gain with Plasma Parameters in a Plasma Wakefield Accelerator 3076
 
  • P. Muggli, T. C. Katsouleas, E. Oz
    USC, Los Angeles, California
  • I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
 
  Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745. DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345.

Systematic measurements of energy gain as a function of plasma parameters in the SLAC electron beam-driven plasma wakefield acceleration (PWFA) experiments lead to very important understanding of the beam-plasma interaction. In particular, measurements as a function of the plasma length Lp show that the energy gain increases linearly with Lp in the 10 to 30 cm range. Based on this scaling, the plasma was subsequently lengthened to Lp=90cm, resulting in the first demonstration of the doubling of the energy of a fraction of the incoming 42GeV electrons*. The peak accelerating gradient is larger than 40GV/m and is sustained over meter-scale plasma lengths. These measurements also reveal that the optimum plasma density for acceleration is about 2.7·1017/cc, larger than the value predicted by the linear theory for the approximately 20 microns bunch length, confirming that the experiment is conducted in the non-linear regime of the PWFA. Detailed experimental results will be presented.

* "Energy doubling of 42 GeV electrons in a meter scale plasma wakefield accelerator", I. Blumenfeld et. al., Nature, 2006, accepted

 
THPMS040 Correlation of Beam Parameters to Decelerating Gradient in the E-167 Plasma Wakefield Acceleration Experiment 3091
 
  • I. Blumenfeld, M. K. Berry, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345

Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch length and beam waist location were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the decelerating gradient. Limits on the transformer ratio will also be discussed. The results are compared to simulation.

 
FRPMS067 Energy Measurement in a Plasma Wakefield Accelerator 4168
 
  • R. Ischebeck, M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  Funding: DOE DE-AC02-76SF00515 (SLAC), DE-FG02-92-ER40745, DE-FG03-92ER40745, DE-FC02-01ER41179, DE-FG03-92ER40727, DE-FG02-03ER54721, DE-F52-03NA00065:A004, DE-AC-0376SF0098, NSF ECS-9632735, NSF-Phy-0321345

Particles are leaving the meter-long plasma wakefield accelerator with a large energy spread. To determine the spectrum of these particles, four diagnostics have been set up. These were used to determine energies of the particles that gain energy in the plasma, those that lose energy by driving the wake and the self-injected particles that are accelerated from rest.

 
FRPMS070 Emittance Measurement of Trapped Electrons from a Plasma Wakefield Accelerator 4183
 
  • N. A. Kirby, M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  Funding: This work was supported by the Department of Energy contracts DE- AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745. DE- FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345

Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC showed trapping of plasma electrons. These trapped electrons appeared on an energy spectrometer with smaller transverse size than the beam driving the wake. A connection is made between transverse size and emittance; due to the spectrometer?s resolution, this connection allows for placing an upper limit on the trapped electron emittance. The upper limit for the lowest normalized emittance measured in the experiment is 1 mm·mrad.