Edge plasma analyses for KSTAR divertor design

The reduction of peak heat fluxes on KSTAR (Korea Superconducting Tokamak Advanced Research) divertor plates is required to meet the requirements of <3.5 MW/m² heat flux and average and peak tile temperatures of <600°C and <1200°C, respectively, since numerical simulations give peak heat fluxes of 24.5 MW/m² for the initial heating power of 15.5 MW with no impurity. The radiative divertor simulation obtained with neon concentration of 1.85% could collapse electron temperature and target plate heat flux well below the requirement. Z_eff at core boundary was ~3. Study on geometry optimization shows that 7 cm of outboard pumping gap gives the best gas throughput and gas throughput can be improved by the proper selection of pumping shape. Core ionization could be reduced by a factor of 2 with inner bump structure. The effects of inboard pumping gap and cryopump are negligible compared to the outboard ones