• P. Muggli
  UCLA, Los Angeles, California
• B.A. Allen
  USC, Los Angeles, California
• M. Babzien, K. Kusche, J.H. Park, V. Yakimenko
  BNL, Upton, Long Island, New York

Funding: Work supported by US Department of Energy.

One of the challenges for plasma wakefield accelerators (PWFAs) is to accelerate a trailing bunch with a narrow energy spread. The real challenge is to produce a bunch train with a least one drive bunch and one trailing bunch. We have demonstrated experimentally at the BNL-ATF a mask technique that can produce trains of bunches with variable spacing in the sub-picosecond range*. This 60 MeV train with one to five drive bunches and a trailing bunch propagates in a 1 to 2 cm long plasma capillary discharge with a variable plasma density. When the plasma density is tuned such that the plasma wavelength is equal to the drive bunches spacing the plasma wakefield is resonantly excited. The distance between the last drive bunch and the trailing bunch is one and a half time that between the drive bunches, putting the trailing bunch in the accelerating phase of the wakefield. The resonance is characterized by a maximum energy loss by all the drive bunches and maximum energy gain by the trailing bunch. Experimental results will be presented.

*P. Muggli et al., Phys. Rev. Lett. {10}1, 054801, 2008

• B.A. Allen, P. Muggli
  USC, Los Angeles, California
• C. Huang
  UCLA, Los Angeles, California
• T.C. Katsouleas
  Duke University, Durham, North Carolina
• V. Yakimenko
  BNL, Upton, Long Island, New York

Funding: Work supported by US Department of Energy.

Current Filamentation Instability, CFI, (or Weibel instability) is of central importance for relativistic beams in plasmas for the laboratory, ex. fast-igniter concept for inertial confinement fusion, and astrophysics, ex. cosmic jets. Simulations, with the particle-in-cell code QuickPic, with a beam produced by an RF accelerator show the appearance and effects of CFI. The instability is investigated as a function of electron beam parameters (including charge, transverse size and length) and plasma parameters (density and length) by evaluating the filament currents and magnetic fields. We present simulation results, discuss further simulation refinements, suggest criteria and threshold parameters for observing the presence of CFI and outline a potential future experiment.