Study of the Beam Divergence in Diamond Field Emitter Array Cathodes

We present the results of beam divergence studies for the diamond field emitter array (DFEA) cathodes producing high-current-density electron beams. At Los Alamos National Laboratory (LANL), we fabricate and test the micrometer-scale diamond pyramids with nanometer-scale sharp tips for use as an electron beam source for a compact dielectric laser accelerator. For the beam divergence measurements, we assembled a test stand consisting of a DFEA cathode, a small mesh aperture anode, and a screen representing of a sapphire disk coated with ZnO (AZO) for beam visualization. A negative voltage of about 40 keV is applied to the cathode, and the mesh and the screen are kept at ground. We record the spot size corresponding to the size of the electron beam on the AZO screen past the mesh anode at different mesh to screen distances. We also conduct the beam dynamics simulations with General particle Tracer (GPT). In this paper, we present the results of the experimental measurements and GPT simulations, along with calculations of the beam's divergence.