Modeling of beam-ionized sources for plasma accelerators

When considering intense particle or laser beams propagating in dense plasma or gas, ionization plays an important role. Impact ionization and tunnel ionization may create new plasma electrons, altering the physics of wakefield accelerators, creating and modifying instabilities, etc. Here we describe the addition of an ionization package into the 3-D object-oriented fully parallel PIC code OSIRIS [R.G Hemker, F.S. Tsung, V.K. Decyk, W.B. Mori, S. Lee, and T. Katsouleas, Development of a parallel code for modeling plasma based accelerators, IEEE Particle Accelerator Conference 5, 3672-3674 (1999).]. Using intense beams to tunnel-ionize neutral gas may become a new source of plasma. For the beams whose electrical fields are right above threshold, the optimal gas density for maximize electrical field is about 7 n/sub 0/(n/sub 0/ is the optimal density according to linear theory /spl omega//sub p//spl sigma//sub z//c=2/sup 1/2/ [E164 proposal, unpublished.]). We apply the simulation tool to the parameters of the current E164 [R. Keinigs and M.E. Jones, Phys. Fluids 30, 252 (1987)] Plasma Wakefield Accelerator experiment at the Stanford Linear Accelerator Center (SLAC). We find that tunnel ionization affects the wakefield and energy gain of E-164 experiment.