Speaker
Description
One of the critical challenges facing the design and operation of next-step high-power steady-state fusion devices is to develop a divertor solution for handling power exhaust, which necessitates access to divertor detachment at relatively low main plasma density. Now Japan focuses on the design of Japanese DEMO (JA DEMO) with ITER size. The V-shaped divertor geometry formed by the vertical and horizontal targets, as a potential candidate for JA DEMO, has a good divertor closure and then facilitates the control of divertor heat load and achievement of divertor detachment. However, for the V-shaped geometry, the interaction of the recycled neutrals with the SOL plasma is strongly dependent on the position of strike point, which has a significant effect on the divertor detachment onset or degree. So, it is high priority to explore the underlying neutral distribution and transport for the control of divertor heat load.
In our simulations, two possible ITER-like divertor geometries corresponding to the outer strike point (OSP) on the vertical and the horizontal targets respectively are used to assess the impact of OSP displacement on the divertor plasma behavior by SOLPS-ITER. The seeding rate of radiation impurity neon (Ne) is scanned with the energy flux entering the scrape-off layer (SOL) P_SOL=100MW. The modeling results show clearly that the corresponding heat flux density and electron temperature at the outer divertor target are reduced with OSP switching from vertical to horizontal target, with the lower upstream electron density for divertor detachment onset.
The different divertor plasma behavior for JA DEMO caused by the change of OSP from the vertical to horizontal plate is mainly due to the different recycling behaviors of neutrals in the outer divertor region. When OSP is on the vertical divertor plate, the recycling neutrals are towards private flux region (PFR). However, when OSP is on the horizontal divertor plate near the corner, the recycling neutrals are directed to SOL region by the reflection on the vertical plate, promoting the recycling behaviors of neutrals in the outer divertor region. Therefore, the divertor configuration with OSP on the horizontal divertor plate near the corner can help concentrate more neutrals near the outer divertor region, inducing the larger momentum loss and stronger detachment. Moreover, the V-shaped divertor geometry with OSP on the horizontal divertor plate benefits the control of heat load and electron temperature at the far SOL region.