Stable plasma wakefield acceleration linear collider stages using drive beam induced ion motion and adiabatic density ramps*

Beam driven plasma wakefield acceleration (PWFA) has shown great potential to be the basis for future linear colliders (LCs). PWFA can acheieve high acceleration gradients with high energy transfer efficiency while maintaining low energy spread. For linear collider applications and designs, the witness beam transverse spot sizes and emittances are on the order of hundreds of nanometers with charges around a nanoCoulomb, and would be accelerated over many stages. These beam parameters will cause the ions to collapse during the transit time of the beam. This leads to slice dependent non-linear focusing forces that can lead to drastic emittance growth. However, An et al. (2017) [1] showed that for envisaged parameters the growth could be tolerable within a LC stage. Mehrling et al. (2018) [2] showed hosing of the witness beam is suppressed in this regime due to the non-linear focusing force from the ions. Hildebrand et al. (2018) [3] showed that drive beam induced ion motion can fully eliminate the witness beam hosing and realign it with the drive beam at the cost of emittance growth. We will show that adiabatic density ramps at the entrance and exit of the plasma can match the witness beam in the presence of ion motion as well as realign it with the drive beam while limiting emittance growth, given an appropriate choice of drive beam density.

[1] An et al., Ion motion induced emittance growth of matched electron beams in plasma wakefields, PRL 118 (2017)

[2] Mehrling et al., Suppression of beam hosing in plasma accelerators with ion motion, PRL 121 (2018)

[3] Hildebrand et al., Mitigation techniques of witness beam hosing in plasma-based acceleration, Proceedings of the Advanced Accelerator Conference, Breckenridge, CO (2018)