Inhibition of Current-spike Formation Based on Longitudinal Phase Space Manipulation for High-Repetition-Rate X-ray FEL

TL;DR

This paper presents a novel method using a dual-mode buncher and beam dynamics optimization to control the longitudinal phase space in high-repetition-rate XFELs, significantly improving peak current and FEL pulse energy.

Contribution

It introduces a new approach combining phase space correction and optimization to suppress current spike formation in high-repetition-rate XFELs.

Findings

Achieved electron bunch peak current of 1.6 kA for 100-pC charge.

Increased FEL pulse energy by over 3 times in simulations.

Effectively manipulated longitudinal phase space to prevent current spike formation.

Abstract

The formation of a double-horn current profile is a challenging issue in the achievement of electron bunch with high peak current, especially for high-repetition-rate X-ray free-electron lasers (XFELs) where more nonlinear and intricate beam dynamics propagation is involved. Here, we propose to correct the nonlinear beam longitudinal phase space distortion in the photoinjector section with a dual-mode buncher. In combination with the evolutionary many-objective beam dynamics optimization, this method is shown to be effective in manipulating the longitudinal phase space at the injector exit. Furthermore, the formation of the current spike is avoided after the multi-stage charge density modulation and electron bunch with a peak current of 1.6 kA is achieved for 100-pC bunch charge.Start-to-end simulations based on the Shanghai high-repetition-rate XFEL and extreme light facility demonstrate that the proposed scheme can increase the FEL pulse energy by more than 3 times in a cascading operation of echo-enabled harmonic generation and high-gain harmonic generation. Moreover, this method can also be used for longitudinal phase space shaping of electron beams operating at a high repetition rate to meet the specific demands of different researches.