Discharge Chamber Performance Research Articles

Effects of magnetic field topography on the ion thruster discharge chamber performance

It is the magnetic field topography that determines the ion thruster discharge performance. A three-dimension numerical model of the 20 cm ion thruster discharge chamber was established, and a particle-in-cell method was used to model the discharge process to investigate the effect of the magnetic field topography on the ionization rate and plasma distribution. The results showed that compared with the cylindrical-cusp magnetic field topography, the ring-cusp field made the energetic electrons primarily confined for their increased path length prior to loss to the anode wall and caused the ionization rate to be increased, but the plasma distributed uniformly upstream of the screen grid and the beam flatness was compared to be decreased to 14.8%. When the magnet size was increased and the distance between magnets was changed, the magnetic field contour and the magnetic flux density were modified, and then an improved beam flatness was obtained, from 0.556 to 0.658, by 15.5%.

Analytical Discharge Model for RF Ion Thrusters

A comprehensive 0-D model of the plasma discharge in magnetic ring-cusp ion thrusters was previously developed. The model utilizes conservation of particles into and out of the ion thruster and conservation of energy into the discharge and out of the plasma, and provided the first closed solution for predicting ion-thruster discharge chamber performance. The 0-D discharge model was benchmarked against the performance measured on several ion thrusters, and successfully predicts the discharge loss as a function of mass utilization efficiency. The analytical model has been modified to handle the discharge chamber configurations and the different magnetic confinement physics found in RF ion thrusters. In these ion thrusters, there is no applied magnetic field to provide confinement of the electrons and ions, but the ac magnetic field induced by the inductively coupled RF coil affects the particle confinement and transport and is important in determining the discharge loss and thruster performance. The modifications to the model required to address the physics of RF thrusters will be discussed, and results showing the predicted ion thruster performance will be presented.

カスプ型イオンスラスタにおける電子エネルギー分布の計測システム

Electron energy distribution of the discharge plasma in a cusped ion thruster plays an important role for its discharge chamber performance. Accurate electron energy distribution measurement, particularly in the energy range above the ionization potential, is required to estimate the discharge performance correctly. This Note presents measurement system that is composed of a low-noise detector circuit with a logarithmic amplifier, digital data acquisition and computer system for data analysis. This system enables us to accurately measure the energy distribution even when the measurement is done in noisy environments. The accuracy of the experimental technique and measurement system is discussed. Using the discharge plasma in a cusped thruster, an example demonstrating the measurement system is given.

Dished Accelerator Grids on a 30-cm Ion Thruster

Several closely-spaced dished accelerator grid systems have been fabricated and tested on a 30-cm-diam Hg bombardment thruster and they appear to be a solution to the stringent requirements imposed by the near-term, high-thrust, low-specific impulse electric propulsion missions. The grids were simultaneously hydroformed and then simultaneously stress relieved. The ion extraction capability and discharge chamber performance were studied as the total accelerating voltage, the ratio of net-to-total voltage, grid spacing, and dish direction were varied.