High Mach flow associated with X point MARFE and plasma detachment

High Mach flowsand their formation mechanism in tokamak divertor regions have beenstudied. Numerical calculations using a two dimensional edgeplasma simulation code (the B2-EIRENE code) have been made for theJT-60U open divertor geometry with discharge parameter ranges ofrelatively low input power and L mode experiments. In the high densitycase, typical formation of an X point MARFE, which is accompanied byplasma detachment, has been observed. At the same time, high Machflows appear near the ionization front, where the plasma staticpressure rapidly drops and is far away from the target plates. Redistribution from static pressure to dynamic pressure without alarge momentum loss is shown to be a possible cause of the high Mach flowsobserved in the simulation. In addition, a simple 1-D analytic modelalong the field lines has been applied and the results are comparedwith the B2-EIRENE results in order to identify the formationmechanism of high Mach flows.