The role of divertor pumping combined with full drifts in particle exhaust and divertor plasma

Abstract

The effect of drifts combined with pumping on particle exhaust is assessed using the SOLPS-ITER code package, considering full drifts. Both drifts and pumping speed S can affect particle exhaust. Drifts change the neutral density by influencing plasma flow and the resulting particle recycling. This leads to the accumulation of neutral particles either far away or close to the pump opening location. While the particle exhaust is enhanced as S raises. When the pump opening is positioned at the common flux region (CFR) of the outer divertor (referred to as Pump CFR/OD), particle exhaust is suppressed by drifts in forward Bt, while it is enhanced by drifts in reversed Bt, with fixed S. On the other hand, when the pump is situated in the private flux region (PFR) of the outer divertor (referred to as Pump PFR/OD), particle exhaust is enhanced by drifts in both reversed and forward Bt compared to the case without drifts. Moreover, the effective pumping in reversed Bt is stronger than in forward Bt. In the same Bt direction, Pump PFR/OD has a higher effective pumping than Pump CFR/OD. Increased S results in higher particle exhaust in all Bt direction and pump location cases. The plasma detachment is affected by drifts, S and pump opening location, respectively. For the specified Bt direction and pump opening location case, higher S suppresses plasma detachment. For an identical particle exhaust rate, stronger pumping capacity can promote plasma detachment. Therefore, Pump PFR/OD can more easily achieve outer divertor detachment than Pump CFR/OD in the same Bt direction. Overall, placing the pump at the PFR side of the outer divertor while running in reversed Bt is the best option from the divertor particle exhaust and plasma detachment point of view.