Simulating Output Currents in Gas-Filled Cylindrical Photoemission Driven Cavities

This work presentations a computational experiment simulating irradiation of various materials (including Au, and Ni) in a cylindrical cavity [1]. The cavity is filled with N2 and Ne gasses at pressures ranging from vacuum to 500mtorr. The computation process happens in two steps. First, the electron emission material is irradiated with an input x-ray photon spectrum to produce a photoelectron emission spectrum. This is accomplished using an electron-photon radiation transport code. The photoelectron spectrum, together with the x-ray time pulse and yield, is then used to characterize the electron emission into the gas filled cylindrical cavity that is modeled via an electromagnetic (EM) particle-in-cell (PIC) code. Each irradiated material produces a different photoelectron emission spectrum and drives a current through the experiment that is measured in an output cavity. The effects of plasma dynamics, including plasma formation due to electron impact ionization within the cavity, are studied. The electron emission currents due to photoelectrons as well as due to surface heating are incorporated in the model and are compared to limiting currents. A subset of simulations is compared to experimentally measured currents.