Experimental investigation of plasma structure dynamics in a rotating magnetized plasma

The turbulent regime of a magnetized plasma column in the Mistral device has been studied by means of electrostatic probes. The device produces a sharply defined cylindrical plasma column rotating in an axial magnetic field. The plasma column is surrounded by an edge region extending from the limiter to the walls. In the turbulent state mean density profile shows the presence of a ring surrounding the plasma column, despite ionization happens only in the central part. Mean potential profiles shows an almost rigid body ExB rotation of the plasma column inside the limiter. An experimental study of the structures in the turbulent state of the device has been performed by means of a conditional sampling analysis. Evidences on the formation of structures emanating from the edge of the plasma column and propagating in the region outside the limiter have been collected. The analysis of their spatiotemporal evolution shows the development of spiral structures and their convection in the background plasma to the walls contributing to a large extent both to particle and to energy transport. The analysis shows that intermittently, triggered by deformation of the profile in correspondence to the limiter position, a tail starts to develop, extending outwards and bending due to the lower angular velocity in the limiter region. The tail firstly grows up to reaching the walls and then vanishes with a lifetime of 200 ms. Time series of conditionally sampled Langmuir probe characteristics have been obtained too, in order to extract the simultaneous spatiotemporal evolution of electron density, temperature and plasma potential. The time series of the plasma potential in the turbulent state shows that a poloidal electric field develops inside the structure convecting radially outwards the plasma. Real time imaging of plasma turbulence in the Mistral device was achieved, with sampling rates of 200 kHz, and employed to obtain spatiotemporal evolution of single structures out of the turbulent state. Preliminary results show that the correlation with the findings obtained from electrostatic probe diagnostics is quite encouraging.