Design strategies for single-cycle ultrafast electron guns

After the first introduction of ultrafast electron guns for acceleration of particles using single-cycle electro-magnetic pulses, the basic structure has gained increasing interest as promising solutions for high gradient compact electron guns. The significant benefit of using transient ultrashort pulses in this acceleration scheme opens a realistic path towards gigavolt-per-meter acceleration gradients. In this paper, we present an optimized design strategy for these electron guns. The goal is to estimate the THz energy needed for an optimum device to accelerate electrons at rest to a certain energy using materials that endure a pre-determined maximum electric field. We start with designing a gun delivering 400 keV electron beam energy and discuss different techniques to enhance the performance. Throughout this design process, it is implicitly shown that the concept of single-cycle ultrafast electron guns can apply THz beams with energies in the level of 100–400 μJ to accelerate electrons, which is the state-of-the-art technology in THz radiation sources. Subsequently, upgrading the design to an 800 keV device is outlined, to demonstrate the eligibility of this concept to perform as linac injectors in compact accelerator facilities. (paper)