Investigation of Electron Extraction from a Microwave Discharge Neutralizer for a Miniature Ion Propulsion System

Abstract

To investigate electron extraction through the orifices of a microwave discharge neutralizer, three-dimensional particle simulations have been conducted. The numerical model is composed of a particle-in-cell simulation with a Monte Carlo collision algorithm for the kinetics of charged particles, a nite-difference time-domain method for the electromagnetic fields of 4.2-GHz microwaves, and a finite element analysis for the magnetostatic fields of permanent magnets. The distribution of the current density on the orifice plate obtained from the numerical model is in a reasonable agreement with the measurement result in an experiment. Moreover, the numerical results have indicated that the electrostatic field of the plasma has a dominant influence on the electron extraction although the electrostatic field produces the opposite force of extraction from the bulk plasma toward the orifice plate. The combination of the sheath potential barrier and the magnetostatic field yields the electron trajectories of extraction.

Electron extraction enhancement via the magnetic field in a miniature microwave discharge neutralizer

“…To improve the electron extraction efficiency, we first focused on the orifice shapes. In previous studies, 17,18 the E × B drift induced not only electron extraction on the clockwise-side of each orifice but also electron backflow on the counterclockwise side and some electrons were also extracted along the magnetic field lines through the orifice, which primarily occurred in the region approximately |r| ≥ 5 mm inside the orifices. Figure 3 shows schematics of the conventional and two redesigned orifice plates, which are referred to as the cases with four circular orifices, four arc orifices, and two arc orifices, respectively.…”

“…25 As boundary conditions, the potential on the metal and boron nitride (BN) was set to zero and the potential at z = 10 mm was set to 20 V for the electron extraction voltage, which is the same voltage as in our previous experiment. 18 In addition, all electrons and ions disappeared at the wall, the antenna, and other boundaries, where no reflection or charge accumulation was assumed.…”

“…15,16 In addition, we numerically investigated the electron extraction mechanisms through the orifices of the neutralizers, which is also difficult to measure experimentally, and found that the E × B drift caused electron extraction mainly on one side of each orifice 17 and that electrons were also extracted along magnetic field lines. 18 Therefore, it was implied that the electron extraction efficiency depends on the orifice shapes and the magnetic fields. In this study, we attempted to improve the electron extraction efficiency of the MIPS neutralizer by changing the orifice shapes and magnetic fields and investigated the effects of these changes on the electron extraction and the discharge characteristics.…”

Effects of negative ions on discharge characteristics of water plasma source for a miniature microwave discharge ion thruster

“…scitation.org/journal/php curvature drift of electrons due to the magnetostatic field of the permanent magnets. 35 Nevertheless, the distribution of the striped patterns differed because of the presence of negative ions. Without negative ions, the simulated electron density and the potential maintained a stable ring shape with striped pattern structures.…”

Effects of E × B drift on electron transport across the magnetic field in a miniature microwave discharge neutralizer

“…We use a real mass ratio of an electron to an ion, with which some simulations were conducted for xenon plasma discharges 18 and electron extraction of the neutralizer. 19,20 Our calculation model consists of both the plasma discharge region and the vacuum region, so that no assumptions are required for the electron extraction. Moreover, owing to the three-dimensional model, we could simultaneously obtain the fluctuations of the azimuthal electric field and the mirror magnetic confinement in the radial direction, which cannot be performed in the two-dimensional models.…”