An Algorithm for Determining Energy Deposition Profiles in Elemental Slabs by Low ( $\ll 100$ keV) Energy Electrons: An Internal Charging Application

Internal charging/discharging is an important concern for today´s spacecraft. An important tool for tracking charge buildup in slabs of material that includes a self-consistent solution of the electric fields in the material is the NUMIT code. To date, one of limitations on use of that code has been determining the effects for particles with energy less than 100 keV. To correct this, a universal algorithm for determining dose profiles in slabs has been developed for low energy (10 keV les E_i les 100 keV) electrons. This work extends the Tabata algorithm, originally developed for E_i > 100 keV electrons, down to 10 keV. Following a brief review of the NUMIT code, the role the Tabata algorithm plays in NUMIT is discussed. As a first step in extending the algorithm, Monte Carlo simulations were performed to obtain the dose-depth profiles for various incident energies. It was found that for a given target, the dose profiles obtained for the different incident energies can be normalized to a single curve by applying the scaling factors for the depth (x-axis) and energy deposition (y-axis). These scaling factors are dependent both on the incident electron energy and on the target material. In the second step, for each target element, the normalized dose profile was fit with a simple equation and the fitting coefficients obtained. The overall fitting procedure and the parameters obtained for the fit are described in this paper.