Towards Laboratory Astrophsics in Plasma Wakefield Accelerators

From supernovae in distant galaxies to wakefield accelerators in laboratories, the interaction of relativistic particles beams with plasma is relevant to many physical scales. For a sufficiently wide bunch, the plasma can act to break the bunch into narrow filaments. In the case of a predominantly electromagnetic plasma response, this current filamentation instability may generate a sufficiently strong field to form collisionless shocks.

The AWAKE experiment at CERN succesfully demonstrated resonantly driven wakefield acceleration with controlled self-modulation of a narrow proton bunch, which results in a single train of proton bunches. Recent experimental studies moved away from an accelerator configuration by increasing the bunch width above the plasma skin depth, potentially causing filamentation. This work utilizes simulations to understand the different plasma responses in detail. The transition between electrostatic and electromagnetic filamentation modes for a quasineutral bunch is studied and compared to competing wakefield-driven instabilities of a long proton bunch relevant to the experiment. This work deepens our understanding on the extent plasma wakefield accelerators can access the electromagnetic regime relevant to astrophysics.