Seeding of Self-Modulation using Truncated Seed Bunches as a Path to High Gradient Acceleration

TL;DR

This paper introduces teSSM, a novel seeding method using truncated seed bunches to enable controlled high-gradient particle acceleration at higher plasma densities.

Contribution

The authors demonstrate that truncating seed bunches with a relativistic ionisation front enables reproducible self-modulation at higher plasma densities, improving seed wakefield amplitude.

Findings

Self-modulation is reproducible at $n_ ext{pe}=7\times10^{14}\mathrm{cm}^{-3}$ using teSSM.

Truncating seed bunches increases seed wakefield amplitude.

teSSM enables controlled high-gradient acceleration with available seed bunches.

Abstract

This manuscript proposes a method to enable controlled high-gradient particle acceleration when requiring self-modulation of the drive bunch. While electron bunch seeding of self-modulation (eSSM) has been realised at a plasma electron density $n_\mathrm{pe}\cong10^{14}\mathrm{cm}^{-3}$, it has not been demonstrated at higher plasma densities due to limitations of available seed bunch properties. As experimentally shown in this manuscript, truncating available seed bunches with a relativistic ionisation front allows these limitations to be overcome. This seeding method is called truncated electron bunch seeding of self-modulation (teSSM) and experiments confirm that -- when using teSSM -- self-modulation becomes reproducible at $n_\mathrm{pe}=7\times10^{14}\mathrm{cm}^{-3}$. Additionally, the seed wakefield amplitude is also increased, which is known to be advantageous because it shortens the length needed to reach self-modulation saturation. The presented results establish teSSM as a method for achieving controlled, high-gradient particle acceleration with long drivers and available seed bunches.