Numerical parameter studies of ion-thruster-beam neutralization

Ion-thruster-beam neutralization is an essential process of the operation of ion engines. By means of a three-dimensional eletromagnetic particle-in-cell simulation, we carry out parameter studies of the basic plasma physics unterlying this process. Special emphasis ist paid to the role of the injection velocity. For the dependence of beam quantities such as electron temperature and beam potential on the injection velocity ratio, we derive scaling laws, which are shown to be in good agreement with measurements taken aboard the Deep Space 1 spacecraft. In particular, the experimentally observed discrepancy between electron temperature and beam potential is reproduced by our simulations and is found to be coused by a quasi-Fermin-deceleration of the electrons at the boundary of the expanding ion beam