Power and isotope effects in the ITER Baseline Scenario with tungsten and tungsten-equivalent radiators in DIII-D

Abstract FEC 2023 contribution: Experiments in DIII-D document the ITER Baseline Scenario (IBS) at q95 ~ 3 and PIN/PLH ~ 1-2, in both deuterium and hydrogen utilizing Kr and Xe as Tungsten-equivalent radiators. The power threshold for H-mode operation (PLH) was found to be about a factor of two higher than the scaling law. In recent IBS experiments in deuterium, intrinsic levels of metals such as Tungsten (W) or molybdenum and inconel are present that reduce the pedestal pressure by 20-25%. A complete radiative collapse of deuterium IBS plasmas occurs at W core concentrations CW = 10-5. Simulations show that for core temperatures expected for ITER, the plasmas would not have a radiative collapse at CW = 1x10-5, moreover Q = 8-10 would still be achieved for CW up to 3x10-5. In contrast to deuterium, the IBS in hydrogen is not affected by intrinsic high-Z impurities. Krypton was injected in a matrix scan of input power and impurity flow in IBS hydrogen discharges. Krypton impurity density profiles in hydrogen are similar to deuterium plasmas, but at Kr flows that are 2-3 times higher for the same input power. Krypton is transported into the core and affects the whole radius; at the highest injection rates a radiative collapse occurs at core radiation fractions of 0.3-0.35, consistent with the expected maximum W radiation fraction for ITER core plasmas. Comparing the results with previous ITPA database studies of the IBS confirms that at higher radiation fraction due to high-Z impurities, a drop in H98 of >10% is observed. On the other hand, the results using Kr as a W-equivalent radiator indicate that metal (W) devices at lower core temperatures than ITER may provide overly pessimistic performance extrapolations to ITER for deuterium-tritium operation.