Software for Modeling and Design of Diamond Amplifier Cathodes

The successful operation of the Department of Energy (DOE) next generation X-ray light sources and accelerator facilities depends on developing reliable photocathodes with long lifetime for production of low emittance, high-brightness, high-average current electron beams. Experiments have already demonstrated the potential to generate amplified electron beams from diamond with peak current density greater than 400 mA/mm2 and average current density larger than 100 mA/mm2 but how to optimize the emission from rough surfaces with negative electron affinity is still to be understood. Physics based simulations of diamond amplifiers can offer valuable insight into their operation, provide guidance to experimental approaches and help their design optimization, however, there are currently no available codes that offer these capabilities. General statement of how this problem or situation is being addressed. Charge generation and transport in bulk diamond can now be simulated with the three dimensional code VORPAL but it lacks algorithms for high-fidelity modeling of surface effects and electron emission from diamond. We will develop and implement algorithms for accurate modeling of electron emission from diamond surfaces with negative electron affinity, surface physics phenomena (including quantum mechanical effects), and metal-semiconductor contacts within VORPAL to enable end-to-end simulations for design of diamond-amplified electron sources. What was done in Phase I? We investigated and implemented two proof-of-concept algorithms for electron emission with realistic surface potentials. We verified the prototyped algorithms and compared results from VORPAL simulations with them to experimental data. These results demonstrate the importance of the new capabilities to better understand the physics of electron emission from diamond surfaces. What is planned for Phase II? We will complete the implementation of accurate, quantum mechanical, modeling of electron emission processes, surface region localized states and space-charge effects, surface roughness, and varying electron affinity to enable realistic investigation of electron emission from diamond via simulations. New experiments are being designed to collect data for validation of the implemented models. We will run extensive simulations to compare with experimental data and investigate energy distribution, emittance, and time response properties of electrons emitted from diamond. Commercial applications and other benefits The proposed new modeling capabilities will aid researchers in developing electron sources that meet or exceed the desired operational parameters for future DOE facilities. This project will produce commercial quality software, including a state-of-the-art graphical user interface, and will allow the VORPAL code to increase its potential for generating further commercial revenue when used in the industry to design both diamond cathodes and semiconductor devices.