Particle Beam Waist Location in Plasma Wakefield Acceleration

The role of beam waist location in interactions between a plasma and a particle beam is not yet fully understood. Nonlinear effects with the plasma make an analysis of such interactions difficult. Five simulations are presented in this report, with the waist location of a beam of ultra-relativistic electrons propagating through one meter of self-ionized lithium plasma. The simulation parameters are chosen to model the recent experiment 167 at the Stanford Linear Accelerator, relevant to the design of future plasma wakefield accelerating afterburners. It is found that beams focused near the point of entry into the plasma propagate further into the plasma and accelerate witness particles to a greater maximum energy before disintegrating. These results could indicate that ion channel formation is dependent on the drive beam waist location and that the plasma accelerating medium can have an observable effect on the focusing of the drive beam. Editorial Note: The research outlined below is the second part of a report that began in the March 2007 issue. IV. METHODS: E-167 EXPERIMENT The E-167 experiments are a series of tests of technology to be used in future afterburners. These tests began in 2005 at the Stanford Linear Accelerator Center (SLAC), and are currently in operation. Complete data from the experiments is forthcoming; however, preliminary results have already demonstrated energy doubling of some particles in the 42 GeV drive beam over a distance of 1 meter.