Ion velocimetry measurements and particle-in-cell simulation of a cylindrical cusped plasma accelerator

The Stanford Cylindrical Cusped Field Thruster (CCFT) has been experimentally and numerically investigated with particular focus on the exit plane acceleration region near the top magnetic cusp. Time-averaged xenon ion laser-induced fluorescence measurements using the 5d[4](7/2) - 6 p[3](5/2) (lambda = 834.72-nm air) Xe II transition have mapped the total ion velocity vectors in this region. The thruster is also simulated using the fully kinetic 3-D particle-in-cell code F3MPIC. The consistent experimental and numerical results give physical insight into the mechanisms of ion acceleration and the role of the magnetic field topology in determining ion trajectories and plume divergence. The electrons are strongly magnetized and follow the magnetic field structure, grouping near the cusps. A steep potential drop over a few millimeters near the exit plane follows the magnetic separatrix of the top cusp, and is consistent with measured ion velocity vectors. A characteristic conical region of high ion density, peak ion velocity, and visible emission is observed in the experimental and simulated plume, with an estimated divergence half-angle of 30 degrees.