Nanodiamond Thin Film Field Emitter Cartridge for Miniature High-Gradient Radio Frequency ${X}$ -Band Electron Injector

The complete design, fabrication, and performance evaluation of a compact, single-cell, ${X}$ -band (~9 GHz) electron injector based on a field emission cathode (FEC) is presented. A pulsed electron beam is generated by tens of kilowatts of radio frequency magnetron signals from a plug-in thin film nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) FEC cartridge. Testing of the ${X}$ -band injector with the (N)UNCD FEC was conducted in a beamline equipped with a solenoid, Faraday cup, and imaging screen. The results show that typically the (N)UNCD FEC cartridge produces $\pmb {\gtrsim }1$ mA/cm 2 at a surface electric field of 28 MV/m. The diameter of the output beam generated from the 4.4-mm diameter (N)UNCD cartridge can be as small as 1 mm. In terms of its practical applications, the demonstrated ${X}$ -band electron injector with the (N)UNCD plug-in FEC can serve as a source for X-ray generation, materials processing, or can be used to drive slow wave accelerating structures. The results presented also suggest that this field emitter technology based on planar (N)UNCD thin films, which are simply grown on the surface of optically polished stainless steel, can enable a vast number of device configurations that are efficient, flexible in design, and can be packaged with ease.