Plasma Dark Current in Plasma Wake Field Accelerators (PWFA)

Evidence of particle trapping has been observed in a beam driven Plasma Wake Field Accelerator (PWFA) experiment, E164X, conducted at the Stanford Linear Accelerator Center. Trapped electrons are observed when the wake field amplitude is above a certain threshold. Trapped electrons in plasma accelerators are the equivalent of the dark current in RF accelerators. Calculations show that the trapping threshold is lower in the case of a plasma field ionized by the electron bunch itself than in a pre-ionized plasma. Experimental and simulation results will be presented.