Ampere-class Bright Field Emission Cathode Operated at 100 MV/m

TL;DR

This paper demonstrates a novel ultra-nano-crystalline diamond cathode operating at 100 MV/m, achieving high charge, surpassing traditional limits, and providing a promising high-gradient source for advanced RF and microwave systems.

Contribution

It introduces a UNCD-based field emission cathode capable of operating at 100 MV/m with high charge and brightness, surpassing the Child-Langmuir limit in an L-band injector.

Findings

Achieved 38 pC charge per RF cycle at 100 MV/m

Surpassed the 1D Child-Langmuir limit under high-gradient operation

Estimated beam brightness of 10^{14}-10^{15} A/m^2×rad^2

Abstract

High current bright sources are needed to power the next generation of compact rf and microwave systems. A major requirement is that such a source could be sustainably operated at high frequencies, well above 1 GHz, and high gradients, well above 100 MV/m. Field emission sources offer simplicity and scalability in a high frequency era of the injector design, but the output rf cycle charge and high gradient operation remain a great and largely unaddressed challenge. Here, a field emission cathode based on ultra-nano-crystalline diamond or UNCD, an efficient planar field emission material, was tested at 100 MV/m in an L-band injector. A very high charge of 38 pC per rf cycle (300 nC per rf pulse corresponding to rf pulse current of 120 mA) was demonstrated. This operating condition revealed a space charge dominated emission from the cathode and revealed a condition under which the 1D Child Langmuir limit was surpassed. Finally, a beam brightness of $\sim 10^{14}-10^{15}$ A/m$^2\times$rad$^2$ was estimated.