Experimental determination of the electron energy anisotropy inside an electron-driven magnetic nozzle thruster

Electrodeless electron-driven magnetic nozzle (ed-MN) thrusters are an interesting alternative to more widespread electric propulsion technologies, such as gridded ion thrusters or Hall effect thrusters, due to their ability to generate thrust without relying on accelerating grids or cathode neutralizers, thus potentially reducing erosion and poisoning issues, especially when used with alternative propellants such as iodine or air.

ed-MN thrusters are based on the conversion of perpendicular to magnetic field gyrokinetic electron energy into parallel electron energy. Thrust is then produced by the acceleration of unmagnetized ions through the ambipolar electric field generated by the difference in mobility between electrons and ions. There is still a reduced understanding of the various phenomena driving ed-MN physics that could help improve thruster performance. While electron energy anisotropy is considered one of the crucial aspects, its experimental observation is still scarce.

In this work, we access the anisotropic electron properties inside an electron cyclotron resonance (ECR) thruster by combining experimental 2D electron density maps with direct thrust measurements. Preliminary results show that electron temperature perpendicular to the magnetic field can be several times larger than the parallel temperature in the thruster source. Such a high anisotropy is probably due to the ECR heating mechanism. Large anisotropy ratios seem to be related to high thruster efficiencies.