Studies of edge plasmas in an anchor minimum-B region of the GAMMA 10 tandem mirror

Results of edge plasma investigation in a minimum-B region of the GAMMA 10 tandem mirror are described. In this experiment, the spatial profile of the ion saturation current and the floating potential in the edge plasmas are measured by using arrays of Langmuir probes installed on conducting plates in anchor cells together with a movable probe near the plate in the east anchor cell. From these measurements, a significant asymmetry to the axis of the plasma was observed in both probe currents and floating potentials. It is also found that there are some impurity-deposited layers partially observed on all the conducting plates and that their locations show a rotational symmetry to the magnetic axis at 180°. In this region, a strong gradient of the magnetic field strength toward the axis exists. The direction of the expected plasma shift corresponds to the ∇→B and curvature drift for ions. The results of ion orbit calculation taking account of the above effect show a good agreement with the measured results.