High Mach flow associated with X point MARFE and plasma detachment

High Mach flows and their formation mechanism in tokamak divertor regions have been studied. Numerical calculations using a two dimensional edge plasma simulation code (the B2-EIRENE code) have been made for the JT-60U open divertor geometry with discharge parameter ranges of relatively low input power and L mode experiments. In the high density case, typical formation of an X point MARFE, which is accompanied by plasma detachment, has been observed. At the same time, high Mach flows appear near the ionization front, where the plasma static pressure rapidly drops and is far away from the target plates. Redistribution from static pressure to dynamic pressure without a large momentum loss is shown to be a possible cause of the high Mach flows observed in the simulation. In addition, a simple 1-D analytic model along the field lines has been applied and the results are compared with the B2-EIRENE results in order to identify the formation mechanism of high Mach flows.