UCLA, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
LANL, Los Alamos, New Mexico, USA
Recent experiments on former facility FFTB at SLAC has demonstrated that a single electron beam driven Plasma Wakefield Accelerator (PWFA) can be produced with an accelerating gradient of 52 GeV/m over a meter-long scale*. If another electron bunch is properly loaded into such a wakefield, it will obtain a high energy gain in a short distance as well as a small energy spread. Such PWFA experiment with two bunches will be performed in FACET, which is a new facility at SLAC**. Simulation results show that with possible beam parameters in FACET the first electron bunch (with less current than that in the FFTB experiment) can still produce a meter-long plasma column with a density of 5x1016 cm-3 via field ionization when we use a gas with a lower ionization energy. The second electron bunch can have a 10 GeV energy gain with a very narrow energy spread. If a pre-ionized plasma is used instead of the neutral gas, the energy gain of the second bunch can be enhanced to 30 GeV.
* I. Blumenfeld et al., Nature 445, 741 (2007).
** M. J.Hogan, et al.,NewJ. Phys.12, 055030(2010).
MPI-P, München, Germany
LANL, Los Alamos, New Mexico, USA
UCLA, Los Angeles, California, USA
USC, Los Angeles, California, USA
LANL, Los Alamos, New Mexico, USA
UCLA, Los Angeles, California, USA
We study numerically the excitation of plasma wakefields by a train of electron bunches using the UCLA particle-in-cell code Quickpic*. We aim to find an optimal regime that combines both the advantages of linear and non-linear plasma wakefield accelerator. On one hand, the longitudinal electric field excited by individual bunches add as in the linear region, and the transformer ratio can be maximized (i.e. much larger than 2) by adjusting the number of particles in the bunches as well as their distance. On the other hand, the bunches create large wakefield independent of transverse sizes evolution while propagating through the plasma as in the non-linear region. In principle, such a scheme can multiply the energy of the witness bunch following the drive bunch train in a single plasma wakefield accelerating stage. The parameters for electron bunches are chosen based on the current experiment at the Brookhaven National Laboratory Accelerator Test Facility (ATF), where this scheme can be tested. Detailed simulation results will be presented.
* C. Huang, J. Comp. Phys.
MPI-P, München, Germany
UCLA, Los Angeles, California, USA
CERN, Geneva, Switzerland
Instituto Superior Tecnico, Lisbon, Portugal
LANL, Los Alamos, New Mexico, USA
BINP SB RAS, Novosibirsk, Russia
USC, Los Angeles, California, USA
HHUD, Dusseldorf, Germany
IPFN, Lisbon, Portugal
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
LANL, Los Alamos, New Mexico, USA
IPFN, Lisbon, Portugal
UCLA, Los Angeles, California, USA
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the after-glow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC* for e- beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the beam density/filaments at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment.
* C. Huang et. al. Journal of Computational Physics 217, 2(2006)
USC, Los Angeles, California, USA
UCLA, Los Angeles, California, USA
In the non-linear or blow-out regime of a plasma wakefield, the electrons of the accelerated bunch oscillate in a pure ion column. It was demonstrated that a single bunch can emit betatron radiation in the keV to MeV range*. In a drive/witness bunch system, the witness bunch can be injected into the ion column with a transverse momentum or initial radial offset, so that the whole bunch oscillates about the column axis as one marcro-electron. This results in a larger emitted power and higher photon energy. The energy loss due to radiation can be compensated for by the energy gain from the wakefield so that the emission process can be sustained over long distance. Detailed results will be presented about the characteristics of the witness bunch oscillations and radiation through numerical simulations** and calculations.
* S.Q. Wang, et al., Phys. Rev.Let., 88(13), 135004,(2002), D. K. Johnson et al., Phys. Rev. Lett. 97(17), 175003, (2006)
** C.H. Huang, et al., J. Comp. Phys., 217(2), 658, (2006)