Transverse envelope dynamics of beam slices in a uniform charged ellipsoidal model of the plasma bubble regime

TL;DR

This paper models the transverse envelope dynamics of electron beam slices in a plasma bubble regime, analyzing oscillations, emittance, and energy spread to optimize particle acceleration conditions.

Contribution

It introduces a uniform charged ellipsoidal model to study beam slice dynamics and provides insights into matching conditions for improved acceleration.

Findings

Transverse envelope oscillations depend on beam and plasma parameters.

Optimal matching conditions minimize emittance growth and energy spread.

Electrostatic fields are modeled as arising from a uniform ion distribution within an ellipsoid.

Abstract

We consider a pair of driver/witness electron bunches propagating in an ionized gas background a configuration similar to the one produced in a capillary discharge where a plasma oscillation has been excited by a driving pulse. We assume as in the plasma nonlinear regime that the plasma electrons behind the driver are completely expelled and an ellipsoidal cavity filled with ions only is formed. The fields are linear in both longitudinal and transverse directions, at least in the region of interest for particle acceleration, as the one produced by a uniform ion distribution within a uniformly charged ellipsoidal volume. The fields produced by the ions and experienced by a witness electron beam are purely electrostatic, being the ions at rest in the laboratory frame on the time scale of interest and it can be represented with the field distribution produced by a 3D charged ellipsoidal. The energy spread and emittance degradation has been studied by slicing the bunch in an array of cylinders and solving envelope equations for each bunch slice. The properties of transverse envelope and emittance oscillations and energy spread degradation have been analyzed together with the related matching conditions for optimal transport and acceleration.