Characterization of diamagnetism inside an ECR thruster with a diamagnetic loop

The plasma-induced magnetic field in an electron cyclotron resonance plasma thruster is measured non-intrusively by means of a diamagnetic loop that encloses the plasma flow. The calibration process is described, and parasitic currents in the thruster walls and plasma oscillations are identified as the dominant sources of uncertainty. The integrated magnetic flux is seen to depend on the applied power and less significantly on the mass flow rate. The effect of the diamagnetic loop radius is also studied by testing two loops of different diameters. To estimate the perpendicular electron pressure in the plasma from the loop measurements, two plasma beam models, 1D and 2D, are used. While both models give similar results for the small loop, they differ significantly for the large loop, showing the relevance of 2D effects when a large diamagnetic loop is used.This work was made in the framework of project MINOTOR that has received funding from the European Union's Horizon 2020 research and innovation program under Grant agreement No 730028. Additional funding came from the Spanish R&D National Plan (Grant No. PN ESP2016-75887)