Magnetically Enhanced Vacuum Arc Thruster for Nanosatellites

Abstract

This dissertation describes the development and testing of a magnetically-enhance Vacuum Arc Thruster (VAT) with various cathode materials and magnetic field strengths. The thruster uses a Power Processing Unit (PPU) used to generate a high-voltage spike to initiate and maintain a high current arc discharge. A multi-layer solenoid coil is placed around the arc discharge to investigate the effects of pulsed magnetic fields on the ion density distribution. The VAT produces consistent arc discharges with a peak arc current of IApk ≈ 270 A with a pulse length of tp ≈ 3.5 ms for three cathode materials, Fe (iron), Al (aluminium), and Cu (copper). The magnetic field generator uses a separate capacitive discharge circuit which produces field strengths between⃗ B = 0 - 250 mT along the center line of the thruster. Research was conducted to determine the effects of applied magnetic fields to the ion density distribution of ions with the VAT plasma plume. Ion-to-arc current ratios were normalised to a baseline VAT to directly compare qualitative distributions for the various materials and magnetic field strengths. The application of a magnetic field results in the increase in peak ion-to-arc current ratios with a decrease in ion-to-arc ratios at higher angles from the center line. The increased peak and narrowing of the ion distribution suggests that the magnetic field causes ion collimation within the plasma plume. For 0 <⃗ B < 250mT, performance increase over the non-magnetic case is observed with the best percentage increase in thrust factor of 16.4% for Al, 10.8% for Cu, and 6.3% for Fe, obtained at⃗ B ≈ 150 mT. For⃗ B > 150 mT, the ion distribution is shown to result in higher ion-to-arc ratios at higher angles perpendicular to the center line resulting in greater momentum loss. The greatest thrust factor increase of Al was found to be as a result of the mass-to-charge ratio of the Al ion which is subjected to greater accelerations due to Lorentz forces. The application of an axial magnetic field was found to increase the thrust factor and result in improved VAT thrust performances.