The effect of the divertor operation regimes on the plasma parallel flow in the edge of a tokamak

Based on the variations of the static pressure along the magnetic field line in different divertor operation regimes, the effects of the divertor operation regimes on the plasma parallel flow at the edge of a tokamak are investigated using a one-dimensional fluid model. In low recycling regime, the variation of the static pressure along the field line is obvious from the scrape-off layer (SOL) region near the X-point, and the variation tendency is the same as that of the density. The Mach number of the plasma parallel flow increases along the magnetic field line and the variation is from gentle to sharp. In high recycling regime, the static pressure does not change much except in the near divertor plate region, as a result, the Mach number of the plasma parallel flow varies gently in the SOL region and the most of the divertor region, and it increases rapidly in the near divertor plate region. The variation of the static pressure in weak divertor detachment regime is similar to that in high recycling regime, but the static pressure shows decrease tendency in the SOL region near the X-point, consequently, the Mach number of the plasma parallel flow at X-point is larger than that in high recycling regime. In strong divertor detachment regime, static pressure decreases obviously in the SOL region and away from the divertor plate region, where the static pressure decreases rapidly, and a high Mach plasma parallel flow is observed. Static pressure decreasing while dynamic pressure increasing to keep the total pressure conservation is shown to be a possible cause of the high Mach parallel flow.