Beam Realignment with Emittance Preservation in a Plasma Wakefield-Accelerator Stage

Plasma-based acceleration linear collider designs consist of many plasma stages where a drive beam drives a wake that accelerates a witness beam. Misalignment between the drive and witness beams can lead to the hosing instability, large emittance growth, and difficulty colliding beams at the final focus. The extreme charge and small spot size of a linear collider class electron beam causes the plasma ions to collapse within their transit time, leading to nonlinear focusing forces. It is shown that drive-beam-induced ion motion can be used to eliminate witness beam hosing and realign it with the drive beam. Fully self-consistent qpad simulations of an initial plasma stage with quasiadiabatic plasma density ramps at the entrance and exit show it is possible to simultaneously match the witness beam in the presence of ion motion while eliminating its centroid offset, at the expense of ∼4% emittance growth. The energy spread growth is limited to <1% and the energy transfer efficiency is 50%.