Investigation of heat flux from non-charged particles in the different divertor closures in DIII-D

A method of using a combination of flush and recessed surface eroding thermocouple (SETC) was develop in DIII-D to independently measure the heat flux to the first wall armor carried by non-charged particles, q_nc, from that carried by charged particles, q_ch. Comparison of heat flux-carrying components in the open divertor and closed divertor is made for the first time in a tokamak. Measurements at lower open divertor of DIII-D showed that q_ch dominates in the attached plasma, while in the detachment conditions, q_nc can contribute up to 50% of the total heat flux near the separatrix. SOLPS modeling results indicate the 2D radiation profile in the SAS divertor significantly changes with the increase of upstream density, which suggests that the location of peak q_nc moves outward along the divertor. The experiments carried out in the SAS-VW divertor suggests the distribution of q_nc is largely dependent on the location and the degree of detachment. As plasma density increases, q_nc decreases near the separatrix while increasing in the far SOL, which is consistent with the SOLPS simulation. In the far SOL region, q_nc may contribute nearly 100% of total heat flux at the divertor surface. Using the new SETC array installed in the SAS-VW divertor, the dependence of q_nc on divertor closure, drift direction and divertor detachment will be systemically investigated in the near future.