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

Abstract

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) 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 Xband 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 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.

Demonstration of Planar Ultrananocrystalline Diamond Field Emission Source Operating in SRF Injector at 2 Kelvin

“…To address this challenge, in this work we explore highly conductive nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] as a field emission cathode material that could complement and simplify fully cryogenic SRF injector designs. (N)UNCD has been proven to be a highly emissive material when tested in normal conducting high gradient L-and X-band injectors [1,2]. Electron emission from the (N)UNCD planar surface with excellent emittance, energy spread, and stability were confirmed.…”

“…Electron emission from the (N)UNCD planar surface with excellent emittance, energy spread, and stability were confirmed. rf pulse currents of ∼1-100 mA were achieved [1][2][3]. At high rep-rate/CW operation, such pulse current range serves as an average current estimate for SRF applications, given that field emission is a quantum tunneling effect (meaning that similar currents are expected between 2 K and room temperature).…”

“…Therefore, the top section of the cathode plug had to be detachable. Similarly to previous L-band and Xband cathode designs [1,2], the top 5 mm of the 8-mm tip was cut: this could allow for quick emitter cartridge sample exchanges for testing. Three options were considered for re-attaching the (N)UNCD coated top section: electron beam welding, indium/lead/tin soldering, mechanical joining.…”

High power conditioning and benchmarking of planar nitrogen-incorporated ultrananocrystalline diamond field emission electron source

“…The field emission cathode (FEC) is a viable choice for rf injectors in many industrial and scientific applications [1][2][3][4][5][6][7][8][9][10]. It has several clear advantages compared to thermionic cathodes and photocathodes.…”