X-11: Hosing Mitigation

Principle Investigator:
Stephan Wesch

Contact in absentia:
Carl Andreas Lindstroem

Description and goals:
In beam-driven plasma wakefield accelerators (PWFA) the efficiency and stability of external and
internal injection techniques are mainly given by the properties of the drive-beam. The bunch
length and peak current are of clear importance in the blow-out regime but a sufficiently good
transverse alignment of each individual slice along the longitudinal bunch coordinate z is mandatory
too. If a slice centroid (a center of mass offset in x, x', y and/or y') exists, the reaction of
the plasma wake may excite the centroid resonantly and lead to hosing instability harming the
blow-out formation and the acceleration of witness bunches.

FLASHForward uses highly compressed, GeV-scale electron bunches generated by the FLASH
linac. Radio-frequency time-dependent coupler-kicks, as well as the unavoidable emission of intense,
coherent synchrotron radiation in the two magnetic bunch compressors and in the extraction
beamline, imprint centroid offsets. A combination of electron beam start-to-end simulations,
which take these effects into account, and particle-in-cell computations of the PWFA process show
severe hosing, compromising an effective operation of the plasma accelerator.

The overall goal of the X-11 experiment is to investigate the hosing instability; both in general
and for FLASHForward in particular. Strategies should be developed and applied to suppress/
mitigate hosing inside the plasma. The main focus lies on the preparation and manipulation
of the electron drive beam. The results will help to improve the design of electron beam injectors
for PWFA and to make PWFA more efficient and reliable.