Abstract
A novel low-power plasma thruster, known as the Halo thruster, is experimentally investigated at the Surrey Space Centre. Deriving from a Hall-Effect thruster concept, the Halo thruster exploits the main features of the E×B acceleration and ionisation mechanisms while aiming at improving performance figures at a low power level. The thruster employs a unique magnetic field topology using a cusped magnetic field with regions of magnetic cancellation and a cylindrical discharge channel geometry. A hollow cathode neutraliser is located either externally or internally along the thruster centreline.
This study involved critical analysis of the Halo thruster concept and upgrading of the propulsion facilities at Surrey Space Centre to include new architectures and diagnostic tools for accurate thruster characterisation and plume investigation. The thruster performance was measured using a novel torsional thrust balance - over a range of power levels (100 W - 1 kW), propellant flow rates (0.5 – 2 mg/s Xe) and cathode configurations –, ranging from 2 to 21 % of anode efficiency, from 150 to 1400 s of anode specific impulse and providing between 2 and 25 mN of thrust. Plasma plume characteristics were analysed using a Wien filter, a Faraday probe and Optical Emission Spectroscopy, and a current probe was used for discharge oscillations monitoring. A phenomenological performance model was derived, and the mechanisms in the plasma discharge that are detrimental to the thruster performance were highlighted. The experimental characterisation and subsequent analysis identified the following main loss mechanisms: low ionisation rates at low discharge voltage levels, significant wall losses and enhanced electron current towards the anode, particularly in the internally-located cathode configuration. The effects of cathode location on thruster loss mechanisms and the role of magnetic null points on plasma confinement within the discharge channel were also analysed and discussed.