High Mach flow associated with plasma detachment in JT-60U

Recent new results of the high Mach flows associated with plasma detachment are presented on the basis of numerical simulations and their comparisons with experiments in JT-60U divertor plasma. The high Mach flows appear near the ionization front away from the target plate. The plasma static pressure rapidly drops, while the total pressure is kept almost constant along the field line near the ionization front, because the ionization front near the X-point is clearly separated from the momentum loss region near the target plate. Redistribution from static to dynamic pressure without a large momentum loss is confirmed to be a possible mechanism of the high Mach flows. It has been also shown for the first time that the radial structure of the high Mach flow near the X point away from the target plate has a strong correlation with the DOD (Degree of Detachment) at the target plate. Also, we have made systematic analyses on the high Mach flows for both the 'Open' geometry and the 'W-shaped' geometry of JT-60U in order to clarify the geometric effects on the flows. The divertor geometry strongly affects the radial profile of the high Mach flows. (author)