DIVERTOR PHENOMENA PRIOR TO DENSITY LIMIT DISRUPTIONS IN JT-60U

Divertor phenomena prior to density limit disruptions have been studied in ohmic and neutral beam heated discharges with power of 7.5-8.5 MW in JT-60U, The MARFE occurs when the outer divertor electron temperature falls down to 10 eV or less for both ohmic and neutral beam heated discharges. The MARFE forms in the vicinity of the X-point, and grows toward the inside of the main plasma accompanied with an increase in particle recycling. The divertor radiation loss during the MARFE stays at a saturation level as a whole though the radiating region changes. After the detachment, the MARFE moves up from the divertor region and repeats the up-down movement in a period of several milliseconds, leading to disruptions.