Kink Instabilities in a Magneto-Plasma-Dynamic Thruster With and Without External Magnetic Field

The properties of plasma fluctuations in a Magneto-Plasma-Dynamic (MPD) thruster and their role on the performance of this kind of devices has been object of an extensive experimental investigation. In particular, the analysis of electrostatic and magnetic fluctuations with and without the application of an external magnetic field has shown the electromagnetic nature of plasma fluctuations. Gross magnetohydrodynamic instabilities are found to develop whenever the current rises beyond a threshold value. 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, generally used in screw pinch stability analysis. The growth of these modes is found to be the cause of the large loss of efficiency observed in MPD thrusters when operating at high current.