Spherical probes at ion saturation in ExB fields

The ion saturation current to a spherical probe in the entire range of ion magnetization is computed with SCEPTIC3D, new three-dimensional version of the kinetic code SCEPTIC designed to study transverse plasma flows. Results are compared with prior two-dimensional calculations valid in the magnetic-free regime [I.H. Hutchinson, PPCF 44:1953 (2002)], and with recent semi-analytic solutions to the strongly magnetized transverse Mach probe problem [L. Patacchini and I.H. Hutchinson, PRE 80:036403 (2009)]. At intermediate magnetization (ion Larmor radius close to the probe radius) the plasma density profiles show a complex threedimensional structure that SCEPTIC3D can fully resolve, and contrary to intuition the ion current peaks provided the ion temperature is low enough. Our results are conveniently condensed in a single factor Mc, function of ion temperature and magnetic field only, providing the theoretical calibration for a transverse Mach probe with four electrodes placed at 45o to the magnetic field in a plane of flow and magnetic field.