2D (r–z) numerical simulations of the plasma and channel erosion in a 100 kW class nested Hall thruster

Results from the first numerical simulations of a nested Hall thruster (NHT) are presented. The X3 is a 100 kW class thruster with one center-mounted hollow cathode and three acceleration channels none of which is currently magnetically shielded. The simulations were conducted with the r–z axisymmetric code Hall2De and focused on operation with all three channels firing, at discharge voltages of 300, 400 and 800 V. The corresponding discharge power levels are 38, 49.6 and 100 kW. A recent experimental campaign provided measurements of the thrust for a wide range of channel combinations and operating conditions, but not at 800 V. At 300 and 400 V, with all three channels operating, the computed thrust is underestimated by 8.4% and 4.7%, respectively. The simulations also allowed for the first estimates of erosion by ion sputtering in a NHT. The maximum erosion rates along the boron nitride channel walls are found to be in the order of 1 mm kh⁻¹ (10³ μm kh⁻¹) at 300 V. The rates at 800 V are a few times higher than those at 300 V. Mechanisms driving the erosion are identified, in part through comparisons with measurements and simulations of a similar single-channel unshielded Hall thruster that has been extensively studied in the past. It is found that anomalous collisions, now widely accepted to drive electron transport in these devices, and the manner in which they develop spatially in the channel interior can play a significant role on the channel erosion. (paper)