Critical regimes and magnetohydrodynamic instabilities in a magneto-plasma-dynamic thruster

An extensive experimental investigation of magnetic and electrostatic fluctuations in a magneto-plasma-dynamic (MPD) thruster, with and without the application of an external magnetic field, has shown that gross magnetohydrodynamic instabilities develop whenever the current rises beyond a threshold value. These instabilities are helical kink modes with azimuthal m and axial n periodicity m/n=1/1 and their occurrence can be described by the Kruskal-Shafranov stability criterion. The presence of these modes is found to be the cause of the loss of efficiency observed in MPD thrusters at high current.