Kinetic simulations of neutral loading processes in electron cyclotron resonance ion sources (ECRIS)

Summary form only given. The loading process of electron cyclotron resonance ion sources (ECRIS) has to be optimized in order to achieve the high currents of highly charged ions required by next generation rare isotope beam facilities. Especially for expensive rare isotopes, high neutral capturing efficiency is desirable to avoid excessive loss to the walls. Kinetic simulations offer a tool to complement experimental investigations of the loading processes, giving access to quantities otherwise difficult to measure. However, the large size of the plasma chambers and the relatively high electron density of ~10¹¹ cm^-3 make these simulations computationally extremely demanding. While a very short time step has to be retained in order to model the electron gyro motion and trapping in the magnetic bottle, higher order particle shapes can relax the additional constraint on the grid resolution, which normally requires the resolution of the electron Debye length in order to avoid numerical instabilities. In addition, Particle-in-cell (PIC), a standard algorithm for self-consistent modeling of plasmas, treats the plasma in the collisionless limit, thus prohibiting simulations of ionization effects. Here we will present simulations of the loading process in ECRIS plasmas using the plasma simulation code VORPAL. We will describe the numerical models, including the collisional model for ionization, recombination and charge exchange, as well as present simulations result for different loading scenarios.