Optical Shaping of Plasma Cavity for Controlled Laser Wakefield Acceleration

TL;DR

This paper demonstrates how shaping the plasma cavity using an elliptical focal spot in laser wakefield accelerators allows for controlled electron beam properties, including charge, profile, and energy, through experimental and simulation methods.

Contribution

It introduces a novel method of transverse plasma cavity shaping with elliptical laser focal spots to control electron injection and beam characteristics in wakefield acceleration.

Findings

Controlled electron beam charge and profile achieved.

Electron energy increased with elliptical focal spot.

Simulations confirmed experimental observations and revealed asymmetric injection dynamics.

Abstract

Laser wakefield accelerators rely on relativistically moving micron-sized plasma cavities that provide extremely high electric field >100GV/m. Here, we demonstrate transverse shaping of the plasma cavity to produce controlled sub-GeV electron beams, adopting laser pulses with an axially rotatable ellipse-shaped focal spot. We showed the control capability on electron self-injection, charge, and transverse profile of the electron beam by rotating the focal spot. We observed that the effect of the elliptical focal spot was imprinted in the profiles of the electron beams and the electron energy increased, as compared to the case of a circular focal spot. We performed 3D particle-in-cell (PIC) simulations which reproduced the experimental results and revealed dynamics of a new asymmetric self-injection process. This simple scheme offers a novel control method on laser wakefield acceleration to produce tailored electron beams and x-rays for various applications.