Beam Dynamics Studies into Grating-based Dielectric Laser-driven Accelerators*

Dielectric laser-driven accelerators (DLAs) based on gratings confine an electromagnetic field induced by a drive laser into a narrow vacuum channel where electrons travel and are accelerated. This can provide an alternative acceleration scheme compared to conventional RF cavity accelerators. Due to the achievable high accelerating gradient of up to several GV/m this could pave the way for future ultra-short and low cost ‘micro’ accelerators. This paper presents detailed beam dynamics simulations for a 100-period dual-grating structure. Using the computer code VSIM the achievable accelerating gradient and final beam quality in terms of emittance and energy spread are discussed. INTRODUCTION Dielectric laser-driven accelerators (DLAs) are promising candidates to shrink the size of particle accelerators. They provide access to accelerating gradients of up to several GV/m due to the higher damage threshold in dielectrics as compared to metals. So far two experiments have successfully demonstrated accelerating gradients of up to 300 MV/m [1] and 690 MV/m [2] for relativistic electrons in fused silica dual-grating structures while accelerating gradients of 25 MV/m [3], 220 MV/m [4] and 370 MV/m [5] were observed in fused silica and silicon structures for the case of non-relativistic electrons. Optimization studies into dual-grating structures have already been performed with the aim to increase the maximum accelerating gradient and optimize the distribution of the electric field inside the structure [6-9]. However, only few studies have been done into the particle beam quality that can be obtained in a DLA, although this is one of the most essential parameters of any accelerator. Investigations into the beam quality of a small electron bunch travelling through a 100-period dual-grating structure have been carried out focusing on the final beam emittance, beam energy spread and maximum accelerating gradient. Simulation were divided into two parts: the first part focused on an electron bunch travelling in the vacuum channel of a grating structure without a laser driving the electric field, while in the second part a laser plane wave was introduced to interact with the electron bunch, as shown in Fig.1. Figure 1 : Schematic of a dual-grating structure. ELECTRON BUNCH IN A DLA WITHOUT A LASER Using the VSIM code [10] for simulation studies, a 100-period dual-grating structure was modelled as shown in Fig.2. The geometry parameters are based on earlier optimization studies [9] and are summarized in the following Table 1. Table 1: Geometry Details of a 100-Period Dual-Grating Structure