# Systematic benchmarking of planar nitrogen-incorporated ultrananocrystalline diamond field emission electron source: rf conditioning and beam spatio-temporal characteristics

## TL;DR

This study systematically evaluates the performance and reliability of nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) as a field emission electron source in RF guns, highlighting its potential for accelerator applications.

## Contribution

It provides a comprehensive benchmarking of (N)UNCD cathodes under RF conditions, including conditioning procedures, emission characteristics, and spatial emission imaging, which was previously lacking.

## Key findings

- Achieved a maximum charge of 15 nC at 42 MV/m in RF gun.
- Identified over 100 isolated emitters per cm² on the cathode surface.
- Demonstrated (N)UNCD's suitability for RF injector applications.

## Abstract

Planar nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, has emerged as a unique field emission source attractive for accelerator applications because of its capability to generate high charge beam and handle moderate vacuum conditions. Most importantly, (N)UNCD sources are simple to produce: conventional high aspect ratio isolated emitters are not required to be formed on the surface, and the actual emitter surface roughness is on the order of only 100~nm. Careful reliability assessment of (N)UNCD is required before it may find routine application in accelerator systems. In the present study using an L-band normal conducting single-cell rf gun, a (N)UNCD cathode has been conditioned to $\sim$42~MV/m in a well-controlled manner. It reached a maximum output charge of 15~nC corresponding to an average current of 6~mA during an emission period of 2.5~$\mu$s. Imaging of emission current revealed a large number of isolated emitters (density over 100/cm$^{2}$) distributed on the cathode, which is consistent with previous tests in dc environments. The performance metrics, the emission imaging, and the systematic study of emission properties during rf conditioning in a wide gradient range assert (N)UNCD as an enabling electron source for rf injector designs serving industrial and scientific applications. These studies also improve the fundamental knowledge of the practical conditioning procedure via better understanding of emission mechanisms.