Simulation study of a photo-injector for brightness improvement in Thomson scattering x-ray source via ballistic bunching

TL;DR

This study demonstrates that adding a short RF linac section behind a photo-injector can significantly compress electron beams, thereby tripling the peak brightness of Thomson scattering x-ray sources with minimal emittance and energy spread increase.

Contribution

The paper introduces a simple ballistic bunching method using an additional RF linac to enhance electron beam peak current and brightness in a typical S-band photo-injector.

Findings

Peak current increases from ~50 A to >300 A.

Peak brightness of x-ray source increases about 3 times.

Minimal increase in emittance and energy spread.

Abstract

Increasing peak brightness is beneficial to various applications of Thomson scattering x-ray source. Higher peak brightness of scattered x-ray pulse demands shorter scattering electron beam realized by beam compression in electron beam-line. In this article, we study the possibility to compress electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve peak brightness of scattered x-ray pulse. Numerical optimization by ASTRA demonstrations that peak current can increase from ~50 A to >300 A for a 500 pC, 10 ps FWHM electron pulse, while normalized transverse RMS emittance and RMS energy spread increases very little. Correspondingly, the peak brightness of Thomson scattering x-ray source is estimated to increase about 3 times.