Ultra nanocrystalline diamond (UNCD) is a promising material for field emitters because of its mechanical and chemical stability, high thermal conductivity, and low electrical resistivity. We proposed to demonstrate fabrication of a special shape field emitter array to produce a sheet electron beam for high frequency vacuum tubes. At Los Alamos, we established a Field Emitter Array Test Stand (FEATS) where we can apply voltages up to 40 kV to test field emitter arrays in a vacuum level of 10^-7 Torr or lower. At this test stand, we can take beam images, measure beam current and study beam divergence. We fabricated diamond cathodes in form of arrays of 1 by 81 pyramids and used them to demonstrate production of a sheet electron beam. This talk will present details of the emission tests and analyses of the produced sheet beam.

The cathodes and RF interaction at extremes (CARIE) is a project in Los Alamos National Laboratory (LANL) that aims for generating a high-brightness electron beam from a high-gradient photocathode. The commissioning of the CARIE facility started in 2022. A 50 MW C-band klystron was conditioned in 2023. A waveguide line including a high-power circulator was constructed and conditioned up to 12 MW in 2024. The facility has new control and logging systems currently being in implementation. An RF injector without a cathode plug was successfully tuned and is ready for installation. This talk will present the progress on commissioning and outlook of the project.

Beam brightness can be enhanced with high gradient operation in photocathode guns. Such high gradient guns, such as the L-band gun at the Argonne Wakefield Accelerator (AWA) facility and the C-band high gradient gun being commissioned in the CARIE project at Los Alamos National Laboratory, are also typically equipped with semiconductor photocathodes due to their high quantum efficiency. To investigate the photoemission process in semiconductor thin-film photocathode under such conditions, we developed Monte-Carlo transport and photoemission models employing electronic, phonon, dielectric and optical properties directly from Density Functional Theory (DFT) calculation, as well as the photo excitation model based on the light interference effect in thin films. This photoemission model is further employed in photocathode gun simulation and used to investigate a recent high-gradient experiment conducted at the AWA photo injector. We will discuss the effects of the high field gradient on photoemission through a comparison of the measurement and the simulated beam dynamics.

Recent simulation work has indicated that next generation photoinjectors will be capable of delivering beams with emittances below 100 nm for bunch charges of a few hundred pico-Coulombs. Experimentally validating these results by measuring such emittances is challenging due to the high resolution required. Additionally, in some cases it is desirable for these characterization measurements to be non-destructive, and to have the capability of selecting subsets of the beam. One technique that has been considered is the use of inverse Compton scattering (ICS) spectra to measure the emittance. Here we present simulation results on the use of ICS to measure 50 nm – 500 nm emittances for a 250 pC bunch charge electron beam.

At Los Alamos National Laboratory, we finalized the design of a 1.6-cell C-band RF photoinjector cavity for the Cathodes And Radiofrequency Interactions in Extremes (CARIE) project. The photoinjector cavity is intended to operate at 5.712 GHz, with an intense electric field on the photocathode up to 240 MV/m, producing 250-pC electron bunches at room temperature. The photoinjector cavity design focused on minimizing the peak electric and magnetic fields. The distributed RF coupling waveguide network design was optimized for achieving minimized vacuum pressure at the photocathode plug emitting surface. We report the RF simulation and vacuum simulation results of the photoinjector cavity. We also discuss the mechanical design considerations related to photocathode plug alignment, laser pipes, and baking out. The designed photoinjector cavity is currently under fabrication.

This talk will outline the potential for commercially available, hollow-core, anti-resonant optical fibers to overcome many of the challenges in creating monochromatic and coherent x-ray sources with laser-electron beam interactions. The differences between inverse Compton scattering and laser undulators will be explored and the immense difficulty in creating a laser undulator outlined. A proposed innovation is to utilize modern day, commercial hollow-core fiber optics to confine the laser and potentially allow for a laser-undulator to be constructed with current state of the art lasers and electron beams. Models of this externally confined laser undulator concept will be presented and plans for upcoming experiments shown.

This poster will discuss the performance of CsTe photocathodes recently grown for the CARIE (Cathodes and Radiofrequency Interactions in Extremes) project at LANL. CARIE requires a low emittance, high quantum efficiency (QE) photocathode, capable of withstanding challenging vacuum conditions and high fields. CsTe is a natural fit. We will describe recent efforts to optimize the co-deposition process after our growth chamber was rebuilt from contamination. We will also show our study of QE from CsTe on different substrates.