Plasma density behavior with new graphite limiters in HT-7

A new set of actively cooled toroidal double-ring graphite limiters has been developed in HT-7 superconducting tokamak for long pulse operation. Significant progress of long pulse operation with the graphite limiter is achieved in HT-7. The operation parameter space is expanded largely, and the edge recycling, plasma density and impurity can be easily handled. The extension of operational region and density behavior with graphite (C) limiters have been studied in this paper. Under the same injected power, the critical density of MARFE onset with the new C limiter is much higher than the previous Mo limiter. A moveable graphite limiter has been developed in order to investigate the local recycling and density limit behavior in HT-7 tokamak, which shows that the recycling is low while plasma is shifted outwards, is high for inwards shift.