The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators

Abstract

Recent proposals for using plasma wakefield accelerators in the blowout regime as a component of a linear collider have included very intense driver and accelerating beams, which have densities many times in excess of the ambient plasma density. The electric fields of these beams are widely known to be large enough to completely expel plasma electrons from the beam path; the expelled electrons often attain relativistic velocities in the process. We examine here another aspect of this high‐beam density scenario: the motion of ions. In the lowest order analysis, for both cylindrically symmetric and “flat” beams, it is seen that for the “after‐burner” scenario discussed at AAC 2004 the ions completely collapse inside of the electron beam. In this case the ion density is significantly increased, with a large increase in the beam emittance expected as a result. We also examine a less severe scenario, where the ion collapse onset is expected, and new, coupled equilibria in the beam and plasma density are created.