Self-consistent simulations of a PWFA linear collider stage with witness beam realignment using adiabatic ramps

Beam driven plasma wakefield acceleration (PWFA) has shown great potential to be the basis for

future linear colliders. Recent progress has shown PWFA can acheieve high acceleration gradients

with high energy transfer efficiency while maintaining low energy spread. In the regime relevant

for linear colliders, the witness beam emittance is ~100 nm and the charge is ~1 nC. With these

parameters, the ion collapse will be drastic and lead to emittance growth, however An et al. (2017)

[1] showed this emittance growth is controllable. Mehrling et al. (2018) [2] showed hosing of the

witness beam is suppressed in this regime due to the BNS mechanism. Hildebrand et al. (2018) [3]

showed that the on-axis ion column formed by a high density drive beam can fully eliminate the

witness beam hosing and realign it with the drive beam. We will show that using density ramps

can help match the beam with the presence of ion motion and realign an oset witness beam. We

will explore the emittance growth of the witness beam using fully self-consistent PIC simulations

using the code QPAD and analytical models.

[1] An et al.,"Ion motion induced emittance growth of matched electron beams in plasma wake-

fields", 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)