X-15: Ionisation

Principle Investigator:
Severin Diederichs

Contact in absentia:
Richard D'Arcy

Description and goals:
The field ionisation process in plasma wakefield accelerators (PWFAs) and the associated dynamics of the newly created plasma particles are, so far, insufficiently understood, despite their importance for the optimisation of PWFAs. This study will concentrate on the field ionisation of a neutral gas by a high-current particle beam and the associated wakefield excitation in the generated plasma with finite radial extent. The wakefields focus the beam and thereby enhance the ionising space-charge field and/or can itself trigger additional ionisation during beam propagation through the gas.

By means of theory and 3D particle-in-cell simulations performed in HiPACE near-threshold ionisation, potentially leading to the generation of exotic wakefields with decoupled longitudinal and transverse field - the magnitude of which may be suitable for the quality-preserving acceleration of witness beams with reduced focusing - will be investigated. This highly nonlinear process will be used as a beam diagnostic to probe the charge density and the beam slice emittance. The FLASHForward X-15 experiment intends to experimentally demonstrate this potential new beam diagnostic, once it has been validated theoretically.