Impact of Tungsten and Tungsten-equivalent radiators on the ITER Baseline Scenario in DIII-D*

DIII-D obtained stationary (2-4 s) ITER Baseline Scenario plasmas with Tungsten (W) and W-equivalent radiators Kr and Xe, which have the same radiative loss rate Lz as W in the hotter

ITER cores, at DIII-D’s IBS temperature T e 2-3 keV. The scenario has now been integrated with radiated fractions expected for ITER f rad 20-40%, while comparing the plasma response to cases with intrinsic metal impurities (W, Mo, Fe) and Kr or Xe. Plasmas with intrinsic metals have a lower confinement than the equivalent Kr and Xe discharges, and a higher susceptibility to radiative collapses, indicating that the behavior of present W-wall machines provide an overly pessimistic assessment of the impact of W in the core of ITER and FPPs. The use of radiators

that mimic the behavior of W in ITER and a comparison with the ITPA world fusion database shows that the operational space at low P in /P LH <1.5 can be opened, being previously inaccessible in W-wall machines. Bolometer and SXR analysis shows that, while W-equivalent radiators enter the core and the “real” metals tends to stay at the edge, the radiation profiles peak in the core much more for the metal impurities, due to their higher Lz values. This mis-match between impurity concentration and radiation profile inhibits the core (sawteeth) and the edge (ELMs) instabilities, in a feedback loop increasing the W core concentration further. The power balance is lost at a core W concentration that is 30 times lower than that of Kr and Xe. Simulations show that, for core temperatures and W concentration expected for ITER, the plasmas would not suffer a radiative collapse, while a fusion gain of Q=8-10 would still be achieved for c W <=3x10 -5 (consistent with the new ITER wall program). This demonstrates the relevance of non-metal materials in tokamaks to mimic reactor conditions, when used in concert with appropriate metal- equivalent radiators.