Experimental Observation of Motion of Ions in a Resonantly Driven Plasma Wakefield Accelerator

TL;DR

This paper experimentally demonstrates that ion motion in a plasma wakefield accelerator depends inversely on ion mass and is driven by the ponderomotive force, affecting wakefield stability during multiple bunches.

Contribution

It provides the first experimental observation linking ion mass and wakefield suppression due to ion motion in plasma accelerators.

Findings

Ion motion depends inversely on ion mass.

Ion motion occurs within a single wakefield event.

Ion motion suppresses wakefields when significant.

Abstract

We show experimentally that an effect of motion of ions, observed in a plasma-based accelerator, depends inversely on the plasma ion mass. The effect appears within a single wakefield event and manifests itself as a bunch tail, occurring only when sufficient motion of ions suppresses wakefields. Wakefields are driven resonantly by multiple bunches, and simulation results indicate that the ponderomotive force causes the motion of ions. In this case, the effect is also expected to depend on the amplitude of the wakefields, experimentally confirmed through variations in the drive bunch charge.