Stable electron beam propagation in a plasma column

Abstract

The stability of plasma-based accelerators against transverse misalignments and asymmetries of the drive beam is crucial for their applicability. Without stabilizing mechanisms, even small initial offsets of the drive beam centroid can couple coherently to the plasma wake, grow, and ultimately lead to emittance degradation or beam loss for a trailing witness beam. In this work, we demonstrate the intrinsic stability of a beam propagating in a plasma column. This result is relevant in the context of plasma-based positron acceleration, where a wakefield suitable for the transport and acceleration of a positron witness beam is generated in a plasma column by means of an electron drive beam. The stable propagation of the drive beam is a necessary condition for the experimental implementation of this scheme. The differences and similarities of stabilizing mechanisms in a plasma column compared to a homogeneous plasma are identified via theory and particle-in-cell simulations. Experimental tolerances are given, demonstrating the experimental feasibility of the scheme.

Self-stabilizing positron acceleration in a plasma column

“…1. The stable propagation of a misaligned electron drive beam has been shown in a recent study [21]. There, the transversely displaced drive beam was found to be attracted to the center of the plasma column.…”

“…Since the scheme relies on cylindrical symmetry, one might expect it to be prone to beam breakup instabilities similar to the ones affecting the hollow core plasma channel. In a recent study [21], the electron driver was found to propagate stably in a plasma column for initial misalignments smaller than the beam size. Still, neither the effect of a misaligned drive beam on the witness beam, nor the stability of a misaligned witness beam itself have been investigated so far.…”