Bimodal Electron Gun R&D

A novel Bimodal Electron Gun is designed to apply microwaves at two harmonically-related frequencies in a half-cell RF gun to increase the RF breakdown threshold. This stratagem is intended to allow the RF gun structure to support a high acceleration gradient as well as to manipulate the emittance evolution in the half cell. The superposition of the harmonic field components can provide an engineered spatiotemporal distribution of the cathode field strength and phase by selecting a proper amplitude ratio and phase relationship between the first and second harmonic RF field components. This approach provides multiple control knobs over the cathode field, bunch length, and bunch charge density, and thus the suppression of the space charge effect and RF nonlinearity. The recent status of the Bimodal Electron Gun R&D is presented, including the designs of the novel two frequency directional coupler and rectangular-to-coaxial mode launchers.