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Planar nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, hasemerged as a unique field emission source attractive for acceleratorapplications because of its capability to generate high charge beam and handlemoderate vacuum conditions. Most importantly, (N)UNCD sources are simple toproduce: conventional high aspect ratio isolated emitters are not required tobe formed on the surface, and the actual emitter surface roughness is on theorder of only 100~nm. Careful reliability assessment of (N)UNCD is requiredbefore it may find routine application in accelerator systems. In the presentstudy using an L-band normal conducting single-cell rf gun, a (N)UNCD cathodehas been conditioned to $\sim$42~MV/m in a well-controlled manner. It reached amaximum output charge of 15~nC corresponding to an average current of 6~mAduring an emission period of 2.5~$\mu$s. Imaging of emission current revealed alarge number of isolated emitters (density over 100/cm$^{2}$) distributed onthe cathode, which is consistent with previous tests in dc environments. Theperformance metrics, the emission imaging, and the systematic study of emissionproperties during rf conditioning in a wide gradient range assert (N)UNCD as anenabling electron source for rf injector designs serving industrial andscientific applications. These studies also improve the fundamental knowledgeof the practical conditioning procedure via better understanding of emissionmechanisms.

physical review. accelerators and beams

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