Acceleration of an electron bunch with a non-Gaussian transverse profile in a quasilinear plasma wakefield

TL;DR

This study uses particle-in-cell simulations to analyze how non-Gaussian transverse profiles of electron bunches affect their acceleration in plasma wakefields, revealing minimal impact on beam quality but potential charge concentration benefits.

Contribution

The paper demonstrates that non-Gaussian transverse profiles have limited effect on beam quality factors but can enhance core charge concentration and symmetry during plasma acceleration.

Findings

Normalized RMS emittance is unaffected by initial transverse shape.

Highly-peaked transverse profiles increase core charge fraction.

Non-axisymmetric beams become symmetric after plasma interaction.

Abstract

Beam-driven plasma wakefield accelerators typically use the external injection scheme to ensure controllable beam quality at injection. However, the externally injected witness bunch may exhibit a non-Gaussian transverse density distribution. Using particle-in-cell simulations, we show that the common beam quality factors, such as the normalized RMS emittance and beam radius, do not strongly depend on the initial transverse shapes of the witness beam. Nonetheless, a beam with a highly-peaked transverse spatial profile can achieve a higher fraction of the total beam charge in the core. The same effect can be seen when the witness beam's transverse momentum profile has a peaked non-Gaussian distribution. In addition, we find that an initially non-axisymmetric beam becomes symmetric due to the interaction with the plasma wakefield, and so it does not cause a detrimental effect for the beam acceleration.