Development and Application of SONIC Divertor Simulation Code to Power Exhaust Design of Japanese DEMO Divertor

Abstract

An integrated divertor simulation code, SONIC, has been developed in order to predict a self-consistent transport solution of the plasma, neutral and impurities in the scrape-off layer (SOL) and divertor. SONIC code has contributed to determining the divertor design and power handling scenarios for the Japanese (JA) fusion demonstration (DEMO) reactor. Radiative cooling scenario of Ar impurity seeding and the divertor performance have been demonstrated to evaluate the power exhaust scenarios with Psep = 230–290 MW. The simulation identified the decay length of the total parallel heat flux profile as being broader than the electron one, because of the ion convective transport from the outer divertor to the upstream SOL, produced by the plasma flow reversal. The flow reversal also reduced the impurity retention in the outer divertor, which may produce the partial detachment. Divertor operation margin of key power exhaust parameters to satisfy the peak qtarget ≤ 10 MWm−2 was determined in the low nesep of 2 − 3 × 1019 m−3 under severe conditions such as reducing radiation loss fraction, i.e., f*raddiv = (Pradsol + Praddiv)/Psep and diffusion coefficients (χ and D). The divertor geometry and reference parameters (f*raddiv ~ 0.8, χ = 1 m2s−1, D = 0.3 m2s−1) were consistent with the low nesep operation of the JA DEMO concepts. For either severe assumption of f*raddiv ~ 0.7 or χ and D to their half values, higher nesep operation was required. In addition, recent investigations of physics models (temperature-gradient force on impurity, photon transport, neutral–neutral collision) under the DEMO relevant SOL and divertor condition are presented.