Ultraviolet tomography of kink dynamics in a magnetoplasmadynamic thruster

In this paper the results of a project concerning the ultraviolet (UV) imaging of a plasma for space applications, produced in a magneto-plasmadynamic (MPD) thruster, are presented. MPD are a class of high-power electric space propulsion devices that accelerate a plasma to high velocities (>10 km/s), by exploiting the Lorentz force. This force arises from the interaction between the discharge electrical current and a self induced and externally applied magnetic field. The imaging system has been realized by inserting three arrays of UV-enhanced photodiodes directly into the plastic structure of the anode. The amplifiers are miniaturized and built into the detector. This advanced diagnostic design allows for a detailed tomographic reconstruction of the emissivity spatial structure, both in the axial direction z (corresponding to a wave number n) and azimuthal direction (wave number m) with high time resolution. A magneto-hydrodynamic instability, with mode numbers m = 1 and n = 1 has been observed, which might affect the performances of the thruster.