Experimental studies of helicon double layers for future high power plasma propulsion

The Helicon Double Layer Thruster (HDLT) concept, invented by Charles and Boswell at the Australian National University (ANU), appears to be promising for future high power electric propulsion, and needs to be investigated further. The original concept (strongly diverging magnetic field in pure argon) has been tested experimentally in a helicon reactor installed at LPTP. The double layer has been found in the same parameter space as at ANU, thus verifying their findings. The specific impulse and thrust estimates derived from flux and energy measurements in the LPTP reactor are rather low, but it is expected that these values can be improved considerably with further research. The effect of adding an electronegative gas has also been Investigated experimentally. In that case, the DL was easily formed, with or without magnetic field. However, it was unstable in a wide parameter range. Performance estimates indicate that it is less promising than the original HDLT concept. Further numerical simulation and experimental work needs to focus on scaling to higher power and proving that the HDLT can function in free space vacuum conditions.