HIGH DENSITY OPERATION CLOSE TO GREENWALD LIMIT AND H MODE LIMIT IN ASDEX UPGRADE

摘要

The L mode and H mode density operational window in the vicinity of the density limit has been investigated with a combination of gas puff refuelling and improved fine tuning of neutral beam injection (NBI) heating power. In this way, a novel strategy is achieved by means of a parallel increase of density and heating power. As the density limit is approached, H modes degrade into L modes independently of heating power; this is in contrast to the generally accepted L → H mode threshold scaling P_heat~L→H　∝ n-bar_eB_t. Furthermore, contrary to the well known heating power independent Greenwald limit, the L mode density limit increases moderately with rising heating power, n-bar_e~DL ∝ P_heat~0.3±0.1 if a simple power law is assumed.