13Three-dimensional particle simulations have been conducted to analyze the mechanisms of 14 electron extraction through the orifices of a 4.2 GHz microwave discharge microneutralizer, 15 using a xenon electron cyclotron resonance plasma. The dimensions of the neutralizer are 16 20×20×4 mm 3 , and a ring-shaped microwave antenna and permanent magnets are employed for 17 its discharges. The numerical model is composed of a particle-in-cell simulation with a Monte 18 Carlo collision algorithm for charged particle motions, a finite-difference time-domain method 19 for microwaves, and a finite element analysis for magnetostatic fields. The simulation results 20 microspacecraft, HODOYOSHI-4. 8) The microspacecraft was launched on June 19, 2014 and 36 the MIPS was operated successfully in space on October 28, 2014 for the first time in the world. 37The neutralizer of the MIPS is based on a low-power microwave neutralizer for the 150-mA-38 class ion beam exhausted from an ion thruster, [9][10][11] and employs the same frequency of 4.2 GHz 39 and ring-shaped permanent magnets, but a different type of microwave antenna is used because 40 of the small size of the MIPS neutralizer. 12) 41Although the MIPS has already been operated in space, the mechanism of electron 42 extraction from its neutralizer is still unclear and needs to be elucidated for a better performance. 43Owing to its small size, the neutralizer operates using an identical discharge chamber, the same 44 4 microwave power, and a half gas flow rate compared with the ion source, which indicates that 45 the MIPS neutralizer consumes resources (space, power, and propellant) more significantly than 46 conventional ion propulsion systems. One of the reasons for its poor performance is considered 47 24) and elastic scattering and charge exchange for ions, 25) where the null-collision method is 79 employed to reduce the calculation time. 26) The motion of excited-state atoms and Coulomb 80 collisions are not taken into account. Neutral particles are assumed to be spatially uniform 81 throughout the simulation and have a Maxwellian velocity distribution at a gas temperature of 82 300 K. (ii) The magnetic fields of microwaves are neglected compared with the magnetostatic 83 fields of the permanent magnets. (iii) The effect of plasma current is not taken into account 84 127The macroscopic parameters, such as electron density and electron temperature, were 128 determined by averaging over 50000 microwave cycles (11.9 µs) after the steady state was 129 reached. The peak plasma density is located in the ECR layer on the right side of the antenna, 130where the maximum electron density is 1.6×10 17 m −3 , and their distributions spread along the 131 magnetic field lines, producing the ring-shaped profile of plasma density. Such a distribution 132 was also confirmed in the experiment. This result indicates that the plasma is well confined 133 because of the mirror magnetic fields. The distributions of electron temperature and plasma 134 potential are almost the same as the d...

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.

No abstract

No abstract

No abstract