Longitudinal dynamics of twin electron bunches in the Linac Coherent Light Source

Abstract

The recent development of two-color x-ray free-electron lasers, as well as the successful demonstration of high-gradient witness bunch acceleration in a plasma, have generated strong interest in electron bunch trains, where two or more electron bunches are generated, accelerated and compressed in the same accelerating bucket. In this paper we analyze a twin-bunch technique in a high-energy linac, such as the Linac Coherent Light Source. This method allows the generation of two electron bunches with high peak current and independent control of time delay and energy separation. We find that the wakefields in the accelerator structures play an important role in the twin-bunch compression, and they can be used to extend the available time delay range. Based on the theoretical model and simulations we propose several methods to achieve larger time delay.