Software for Design of Advanced Alkali-antimonide and Heterostructured Photocathodes

Photocathodes capable of delivering high average current, low emittance, and high brightness electron beams, with a long lifetime and high quantum efficiency are needed for the effective operation of modern accelerator facilities managed by the Department of Energy (DOE). Recent experiments on alkali-antimonide and heterostructured semiconductor photocathodes have demonstrated the potential of these materials to generate electron beams with the targeted properties. The physics of these complex materials with different heterostructured configurations possible is not well understood. We propose to develop software to enable high-fidelity, three-dimensional, modeling capabilities to simulate and design alkali-antimonide and semiconductor heterostructured photocathodes that meet or exceed the desired operational parameters for DOE facilities. We will design and develop software code for modeling of electron generation in alkali-antimonide photocathodes due to absorption of photons with given energies and charge particle transport based on the Monte Carlo approach for treating scattering processes. We will include the important effects of built-in fields due to heterojunctions and band bending in surface space-charge regions. We will model the physics of electron emission using a general approach for treating photocathode surface potentials. The developed models will be implemented to enable end-to-end, high-fidelity three-dimensional simulations of electron generation, transport, and electron emission from alkali-antimonide photocathodes. We will investigate and prototype algorithms for electron generation due to optical excitations, electron scattering with phonons, charge impurities, and other charged carriers. We will explore how to take into account effects of built-in fields due to heterojunctions and surface space-charge regions. We will develop a proof-of-concept prototype simulation of charge generation, transport, and electron emission from an alkali-antimonide photocathode. The proposed new modeling capabilities will be added to VSim, a Tech-X software product, and 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 increase VSim's capability to generate further