Design and verification of a dielectric laser accelerator test system for sub-relativistic electrons

Dielectric laser accelerators (DLAs) can achieve acceleration gradients that are 1 to 2 orders of magnitude higher than traditional radiofrequency (RF) accelerators. Due to the micrometer-scale dimensions of the DLA acceleration structure, on the one hand, high requirements are imposed on the quality of the electron beam and the alignment among the electron beam, driving laser, and DLA in experiments. On the other hand, although the DLA acceleration gradient is very high, the acceleration distance is insufficient, resulting in relatively small absolute energy gain for sub-relativistic electrons after DLA acceleration. These electrons are susceptible to interference from stray electromagnetic fields during propagation, posing significant challenges to the resolution and accuracy of sub-relativistic electron energy spectrum testing. Based on the principle of laser-driven grating-structure DLA for accelerating electron beams, this paper designs a complete test system, constructs electronic dynamics simulation models and magnetic field measurement electron energy spectrum simulation models for verification, designs a double-layer magnetic shunt to shield the interference of leakage magnetic fields on electrons in the simulation, considers factors such as the beam spot radius, divergence angle, and geomagnetic field intensity of the electron beam that conform to experimental conditions, and finally obtains simulated images of electron spots on the fluorescent screen after the electron beam is deflected by the magnetic field. The electron dynamics simulation results show that the electron beam achieves a maximum energy gain of 14.4401 keV over an acceleration length of 36 μm, with an acceleration gradient reaching 401.114 MeV/m. Based on the acceleration effect, a magnetic field of 𝐵𝐵 = 170 Gs is set, and an electron spot after deflection is obtained. The edges of the spots before and after acceleration are separated by Δ𝑑 = 4.2889 mm, and the maximum energy gain measurement error is ε_{ΔΕ'} = 4.45%, realizing precise measurement of the energy gain of sub-relativistic electrons.