UV imaging of a Plasma for Space Applications

In this paper we present recent results of a project concerning UV imaging of a plasma for space applications. Magneto-plasmadynamic (MPD) thrusters 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 a discharge current and both self-induced and externally applied magnetic field. This device is promising for long-range space missions. The imaging system has been realized by inserting 3 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 wavenumber n) and azimuthal direction (wavenumber m) with high time resolution. In fact, recently an intense effort has been devoted to the optimization of the performances of the thruster, which unfortunately shows a limitation of the efficiency at high plasma current IP and applied axial magnetic field Bz. As proposed in [Zuin et al., 2004a], this limitation is not merely confined to the field of engineering, but it unveils genuine physics, in that it is connected to the onset of an (m = 1; n = 1) magneto- hydrodynamic (MHD) kink instability. In this paper we will show new results that confirm the existence of a kink, and extend the analysis of the properties of the MPD plasma column