Thermal Trapping in the Blowout Regime of the Plasma Wakefield Accelerator

The nonlinear, blowout regime of the plasma wakefield accelerator has been the subject of considerable interest due to its potential for use as a next generation accelerator in high energy physics experiments. Much of the analytical work and simulation in this regime has been restricted to scenarios of cold background plasma. Significant theoretical results concerning plasma thermal effects have been obtained only in one dimension. This paper addresses the phenomenon of background electron trapping, in particular by thermal means, and its effects on wakefield development. In order to examine a key source of initial temperature, we also discuss plasma electron heating through the decay of the nonlinear wake waves themselves. Through 2D particle-in-cell simulations, we find that some thermal trapping occurs even at modest plasma temperatures, creating Landau damping of the wakefield that increases rapidly with temperature up to ∼500 eV, and then less strongly for higher temperatures. In addition, the peak electric field produced in the plasma scales linearly with the driving beam charge over a wide range before degrading suddenly once a charge threshold has been reached. These results suggest that temperature is a significant factor in a plasma wakefield accelerator’s effectiveness, and that parameters such as the charge of the driving beam and the injection time of the witness beam should be carefully chosen to minimize negative thermal effects.