High Average Current Bunched Electron Source for RF Accelerators

High-average current high-quality electron beams are imperative for high-power RF accelerators used in various energy and environmental applications in industry, medicine, and national security as well as for advanced existing and future accelerator systems such as PIP II, particle colliders (eRHIC BNL) for cooling high-energy proton, ion, and hadron beams, storage rings, wakefield accelerators (AWA), and energy recovery linacs. The most common current approach to generate high-peak current high-brightness short electron bunches uses photoemission excited by intense laser radiation. However, to avoid overheating of the cavity wall, photocathodes are operated at a subharmonic of the linac frequency that in turn restricts the average beam current. There are also limitations in the electron beam average current due to the average power available from drive lasers. On the other hand, the state of the art thermionic sources that produce high average current electron beams, do not have yet good emission gating methods to realize sufficiently short and good quality electron bunches. General statement of how this problem is being addressed We will develop a robust thermionic electron source of >1 A average current with advanced gating of the emission at the linac-frequency and its 3rd harmonic. Central to the approach is a novel scheme for energy efficient feeding of the 3rd-harmonic power in the RF gap. The cathode will be attached to the gun cavity through this small emission gating gap in which the RF modes will be excited. The use of thermionic emission will allow for the desired high-average current CW electron beams. Adding the 3rd emission-gating-harmonic will shorten the bunches and by this means lessen impact of the RF curvature on the beam quality resulting in the smaller energy spread and bunch emittances. The high current electron beam will be suitable for injection into high-power normal- or superconducting linacs in CW mode at a repetition rate of the linac frequency. What is to be done in Phase I? In Phase I we will focus on modeling, simulations, beam dynamics studies, and baseline design of the electron source and its components including RF structures for gating the emission and for the gun cavity. The developed analytical background and baseline design will allow experimental demonstrations of the electron source of high average current CW bunched beams in Phase II. Commercial Applications and Other Benefits It is anticipated that the electron source will be in demand for normal- and superconducting particle accelerators and will benefit many commercial and energy and environmental applications such as treating waste and potable water, sludge, stack gases, and medical waste as well as X-ray sources for medicine, sterilization, materials processing, and non-intrusive imaging. Key Words: accelerator, electron bunch, emittance, gating, harmonics, RF gun, thermionic emission Summary for Members of Congress This project will develop a high current electron source. It will generate bunched electron beams that can be used for basic research, materials processing, medical, and other applications.