Study of recycling and density limit in the HT-7 superconducting tokamak [rapid communication]

A moveable graphite limiter has been developed in order to investigate the influence of the horizontal plasma position on the density limit in the HT-7 tokamak. The local recycling and density limit behaviour has been studied in this Letter, which shows that if plasma is shifted outwards the recycling is low, for inwards shift is high. For these set of ohmic discharges a maximum Greenwald number, N>1.2, was achieved, when the plasma column was repositioned more than Δ=+2.25 cm outwards. It is important that lower local recycling discharge leads lower radiation power and higher density.