Fusion Science and Technology / Volume 55 / Number 2T / February 2009 / Pages 38-45
Technical Paper / Seventh International Conference on Open Magnetic Systems for Plasma Confinement
Detailed behavior of plasmas has been investigated in the course of an optimization phase of wall conditioning in the central-cell of GAMMA 10 tandem mirror. The results are described based on the visible image measurements using CCD camera together with H line-emission measurements in the central-cell. Three limiters are installed in the central-cell and the behavior of the plasmas near the each limiter is precisely observed in response to electron cyclotron heating (ECH) for potential formation. In an early stage of wall conditioning in GAMMA 10, plasma parameters obtained in standard hot ion mode plasmas are compared in cases of sustained plasma in ECH pulses and of collapsed one simultaneously with ECH. Dependence of gas puffing from the mirror throat in the central cell and of the diameter of limiters is also investigated on the plasma behavior in ECH. From the measured results, it is recognized that a significant upward shift of the plasma column and imbalance of the H intensity between east and west Iris-limiters cause the plasma collapse in ECH. A systematic analysis of the dependence on plasma durability in the number of wall conditioning shots, the position of the plasma just before the ECH injection and suitable quantity of gas puffing is necessary for stably sustaining the plasma during potential formation by ECH.