Electron bunchers for industrial RF linear accelerators: theory and design guide

Abstract The acceleration of electrons in resonant linear accelerators (linacs) typically consists of three main stages: (1) emission of the electrons from the cathode and their pre-acceleration with a DC field to the energy of tens of keV; (2) grouping the DC electron beam into bunches and their synchronization with the correct phase of high-frequency electromagnetic fields, and (3) accelerating the bunches of relativistic electrons to the required energies. Although many books describe the theoretical and practical aspects of electron linac design, most of them concentrate on beam physics in either the gun stage or in the relativistic regime, while leaving the description of the bunching process rather general. The physics of non-relativistic motion is described in the literature on ion accelerators, but in practice, it cannot be scaled to electron machines due to the significantly different particle mass and acceleration rate, beam velocity change, and frequencies. In this tutorial review paper, we will fill this gap with a detailed description of the bunching process and provide practical advice on the design of bunching sections in industrial-grade electron linacs.