A Systematic Study of Impurity Ion Poloidal Rotation and Temperature Profiles Using CXRS in the TJ-II Stellarator

Abstract

A concise systematic study of impurity parameter profiles (impurity ion temperatures and poloidal velocities) measured under different plasma conditions has been carried out in the TJ-II stellarator using an active spectro-scopic diagnostic system covering a large section of the central plasma minor radius, from r/a = 0.3 to 0.85, with high spatial resolution. For this, plasmas using hydrogen as the working gas were created and maintained using electron cyclotron resonance heating (from 400 to 500 kW) and line-averaged densities between 0.4 and 0.9 × 10 19 m −3 were achieved. In the first instance, it is noted that ion temperature profiles tend to be flat across the accessible plasma radius, whilst a transition in the poloidal velocity from the ion to the electron diamagnetic direction is observed with increasing density. At the same time, the shear point for impurity velocity is seen to propagate outwards towards the plasma edge. Similarly, at a fixed density, a similar tendency is observed when raising the injected heating power. These results together with the behaviour of the impurity temperatures for the same conditions, suggest that collision frequency ν