Investigation of two discharge configurations in the CAMILA Hall thruster by the particle-in-cell method

Abstract

The CAMILA (co-axial magneto-isolated longitudinal anode) concept was introduced to improve the ionization efficiency in low-power Hall thrusters. With relatively large coaxial anode surfaces and longitudinal magnetic strength, the CAMILA represents a significant departure from conventional Hall thrusters. In order to investigate the physical processes inside the CAMILA thruster, a two-dimensional particle-in-cell simulation of the thruster channel is used. The discharge parameters are analysed in two magnetic configurations: simplified CAMILA with a conventional magnetic field and full CAMILA with strengthened longitudinal component of the magnetic field. The simulation is fully kinetic with electrons, ions and gas atoms (xenon) represented as particles. Electron-neutral interactions are included together with particle-boundary interactions such as recombination and secondary emission. In addition, dielectric boundaries float and the cathode is represented as a free-space boundary, emitting electrons to satisfy quasi-neutrality on its surface. The high anode efficiency, observed in experiments, can be explained by several mechanisms found in this work. In the simplified case (magnetic configuration similar to the experiments) a focusing potential is created near the anode-dielectric boundary that directs ions away from the walls. It is created due to a combination of anode placement, in parallel with the channel, penetration of the plasma inside the anode cavity and the shape of magnetic force lines. Simulated steady-state results show good agreement with experimental measurements. In the full CAMILA case we demonstrate that the ionization region is found in the anode cavity. The electric field inside the anode cavity is substantial and it is directed towards the anode cavity centreline. Electrons are heated sufficiently to reach a high degree of ionization inside the anode cavity while ion currents to the anode surfaces are reduced significantly.

Characterization of CAMILA Hall Thruster Discharge using Electrical Probe Measurements

“…Similar results were obtained using particle-in-cell simulation in Ref. 15. By integrating the Hall current density over the computation area, in the r-z plane, we obtain the total Hall current: (c) Full CAMILA Figure 14: Spatial distribution of azimuthal current density.…”

“…7, this velocity profile was found using numeric simulation of the gas flow, details of which are provided in Ref. 15. As A ch ≈ 1.62 × 10 −3 m 2 andṁ a ≈ 0.87 × 10 −6 kg/s, we obtain from Eq.…”

“…Similar structure was found in numerical simulations as well. 15 The location of the corridor, closer to the outer anode, can explain the large current collected by the outer anode in this configuration (84 % of the total current). The electron temperature map (Fig.…”

“…Similar concave equipotentials were found in numerical simulations as well. 15 Electric fields derived from these equipotentials are directed toward the middle of the channel; because ion dynamics is determined primarily by the electric fields, the focusing allows to reduce the number of ions lost to the walls, especially in the ionization zone where the ion energy is low. The effects of ion focusing on the radial non-uniformity of the discharge are clearly seen in the current density map (Fig.…”

Effect of Preionization on the Erosion of the Discharge Channel Wall in a Hall Thruster Using a Kinetic Simulation

“…This fully kinetic model can also include the classical and Bohm diffusion mechanisms to predict the correct rate of electron transport, providing a more reliable electron distribution. However, it is numerically infeasible to simulate the corrosion by employing the real physical properties of the Hall thruster [28]. Therefore, some simplifications are developed, such as the artificial mass ratio and permittivity manipulations, to accelerate the simulations.…”