Microwave Thermionic Electron Gun for Synchrotron Light Sources

Conventional thermionic RF guns can offer high average beam current, which is important for synchrotron light and THz radiation sources facilities, as well as for industrial applications. The Advanced Photon Source (APS) at Argonne National Laboratory (ANL) is a national synchrotron-radiation light source research facility that utilizes thermionic RF guns. However, these existing thermionic guns are bulky, difficult to handle and install, easily detuned, very sensitive to thermal expansion and are due for a major upgrade and replacement. In response to this problem, RadiaBeam Systems has designed and built a new, more stable and reliable gun with optimized electromagnetic performance, improved thermal engineering and more robust cathode mounting technique, which is a critical step to improve the performance of existing and future light sources, industrial accelerators, and electron beam driven terahertz sources. During this Fast-Track project, we developed a new thermionic RF gun for APS that offers substantial improvements in reliable operation with a robust interface between the thermionic cathode and the cavity, as well as better RF performance, compared to existing models. This improvement was made possible by incorporating new pi-mode electromagnetic design, robust cavity back plate design, and a cooling system that will allow stable operation at 70 MV/m peak on axis field in the cavity. We successfully fabricated the prototype of the gun, conditioned it for 3 MW RF power at 4μs pulse length and 100 Hz repetition rate, and demonstrated 150 mA beam current at 2.9 MeV at the Injector Test Stand at APS. In this Phase IIB we propose to transition the prototype RF gun towards a market-ready product. In particular, we will develop a simplified design focused around a non-removable back plane to reduce cost and complexity, eliminating over 50 components within the currently complex multi-bellows integrated sub-assembly. Further design modifications will incorporate provisions for improvements to the locating mechanics for the cathode stalk to ensure that it can be repeatably centered to below a 20 micron accuracy. We will also adapt the existing RF design of the gun for different parameters required by other customers that have expressed interest in purchasing this gun. The goal of this project is to build an instrument that will be immediately used by Argonne National Laboratory in their work on improving stable and reliable operation of the Advanced Photon Source. This project also has an immediate impact on an existing joint APS-RadiaBeam THz radiator program, allowing to increase its power and frequency. The gun has attracted interest from other light source facilities such as NSLS-II as well as for industrial (industrial radiography/CT, diamond processing) and security (cargo inspection) applications.