Electric propulsion is an established high-efficiency method in deep space explorers. However, most of the
applied methods feature electrodes in direct contact with the plasma, thus its lifetime is limited by the electrodes’
erosion. We developed electrodeless electric propulsion systems in order to overcome this problem, and
performed optical measurements to estimate the high-density helicon plasma performance of the systems. The
electron and neutral particle density profiles were measured by a high-speed camera, and the velocity of the
singly-charged Ar ions was determined by a high-resolution monochromator. Additionally, a preliminary experiment
of a spectroscopic method using an intensity ratio based on a collisional radiative model with a CCD
monochromator was performed. The plasma parameters were in good agreement with the results obtained by an
electrostatic probe, and the non-invasive optical measurements presented here can constitute an effective tool for
evaluating an electric propulsion system.