Plasma confinement in the GAMMA 10 tandem mirror

Abstract

The central cell density and the diamagnetic signal weredoubled as a result of plug potential formation by ECRH in hot ionmode experiments on the GAMMA 10 tandem mirror. In order toobtain these remarkable results, the axisymmetrized heatingpatterns of ECRH and ICRF heating were optimized. Furthermore,conducting plates were installed adjacent to the surface ofthe plasma along the flat shaped magnetic flux tube located inthe anchor transition regions; the plates may contribute tothe reduction of some irregular electric fields producedpossibly with ECRH in these thin flux tube regions. Theconducting plates contributed to reducing the radial loss rateto less than 3% of the total particle losses, along with improvements in the reproducibility of the experiments and thecontrollability of the potential confinement. The increases incentral cell density and diamagnetism in associationwith the increase in plug potentials scaled well withincreasing ECRH power. A plug potential of 0.6 kV and adensity increase of 100% were achieved using an ECRH power of140 kW injected into both plug regions. The plasma confinementwas improved by an order of magnitude over a simple mirrorconfinement owing to the tandem mirror potential formation.