Seeding of self-modulation using truncated seed bunches as a path to high gradient acceleration

Abstract

This manuscript proposes a method to enable controlled high gradient particle acceleration when requiring self-modulation (SM) of the drive bunch. While electron bunch seeding of self-modulation has been realized at a plasma electron density [L. Verra et al., (AWAKE Collaboration), Controlled growth of the self-modulation of a relativistic proton bunch in plasma, Phys. Rev. Lett. 129, 024802 (2022)], 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 ionization 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. 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.