Nano-Diamond Thin Film Field Emitter Cartridge for Miniature High Gradient Radiofrequency $X$-band Electron Injector

TL;DR

This paper presents a compact X-band electron injector using a nitrogen-incorporated ultrananocrystalline diamond field emission cathode, demonstrating high current density and small beam size suitable for various high-frequency applications.

Contribution

It introduces a novel, simple, and efficient planar (N)UNCD thin film cathode for a miniature high-gradient RF electron injector, with detailed design, fabrication, and performance evaluation.

Findings

Produces >1 mA/cm² at 28 MV/m surface electric field

Generates a beam as small as 1 mm diameter

Suitable for X-ray, materials processing, and RF applications

Abstract

The complete design, fabrication, and performance evaluation of a compact, single cell, $X$-band ($\sim$9 GHz) electron injector based on a field emission cathode (FEC) are presented. A pulsed electron beam is generated by a 10's of kW radiofrequency (RF) magnetron signal 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 $\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, travelling-wave tubes (including GHz and THz backward wave oscillators), 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.