Temporal behaviour of the potential and fluctuations at the L-H transitionon JFT-2M

Potential and density/temperature fluctuations at the L-H transition are me asured by a heavy ion beam probe (HIBP) on JFT-2M. It has been observed tha t the time scale of potential change is as fast as 10-100 mu s when the inp ut power (P-in) is larger than the L-H threshold power (P-th). When P-in = P-th, the confinement is improved step by step, with sawteeth crashes accom panied by a decrease of potential. After a few sawteeth crashes, the potent ial drops rapidly to the level of the ELM-free H-mode. At that time, the de nsity/temperature fluctuations are suppressed simultaneously. The observati ons of the temporal behaviour of the potential and fluctuations in such all L-H transition are reported.