Further Experimental Evidences of the Development of Kink Instabilities in MPD Thrusters

The paper deals with the most recent results of a wide diagnostic activity carried out on two similar gas-fed MPD thrusters, with and without an externally applied magnetic field. Recently it has been shown that large-scale MHD instabilities are found whenever the current rises beyond a threshold value, well predicted by a semi-empirical approach. These instabilities have features of helical kink modes with prevalent azimuthal m and axial n periodicity m=n = 1=1 and their occurrence can be described by the Kruskal-Shafranov criterion. The growth of these modes was found to be the cause of the large loss of efficiency observed in MPD thrusters when operating at high current. In this paper further evidences of MHD instabilities are presented, and a better characterization is obtained by means of an integrated system of both electromagnetic and optic probes, and ultraviolet tomography. This advanced diagnostic design allows for a detailed tomographic reconstruction of the emissivity spatial structure, both in the axial and azimuthal directions