Performance increase of electron cyclotron resonance magnetic nozzle thruster via magnetically thickened resonance region

Electron Cyclotron Resonance (ECR) magnetic nozzle thrusters are a promising technology due to their electrodeless nature allowing for reduced erosion rates and extended lifetimes. Their simple design makes them relatively low-cost, however their typically low performance prevents them from becoming commercially viable. This thesis investigates multiple novel techniques to enhance the performance of ECR magnetic nozzle thrusters. Each is experimentally characterised to determine performance and the physical mechanism by which it is affected.The primary focus of this thesis is investigating the effect of the magnetic field strength gradient at resonance on the thruster performance. It was found analytically that decreasing the magnetic field strength gradient at resonance increases the thickness of the resonance region and the energy transferred from the microwaves to the electrons. This was then investigated experimentally using two different ECR thrusters. Using an electromagnet, the magnetic field strength gradient at resonance was decreased, resulting in an increase in thrust and specific impulse of 60 %, while thruster efficiency was increased by 16 %. By using an iron ring to decrease the magnetic field strength gradient at resonance, instead of an electromagnet, thrust and specific impulse increased by 15 %, while thruster efficiency increased by 32 %.The use of dual microwave frequencies at low-frequency separations was investigated and was found to increase thrust and specific impulse by up to 13 %. The effect of changing the resonance region location was also investigated, with the thrust found to decrease if the resonance region was located in the rear 8 mm of the thruster's 20 mm long chamber. Lastly, a magnetic mirror trap was implemented, which was found to decrease the propellant mass flow rate required for ignition and could increase the performance of miniaturised, low mass flow rate ECR thrusters.