No abstract

No abstract

No abstract

Following ELMy H-mode experiments with liquid metal divertor target on the COMPASS tokamak, we predict the behavior of a similar target on COMPASS Upgrade, where it will be exposed to surface heat fluxes even higher than those expected in the future EU DEMO attached divertor. We simulate the heat conduction, sputtering, evaporation, excitation and radiation of lithium and tin in the divertor area. Measured high-resolution data from COMPASS tokamak were rescaled towards the Upgrade based on many established scalings. Our simulation then yields the amount of released metal which ranges from 4 mg s −1 upto 12 g s −1 depending mainly on the geometry and Li/Sn choice, quite independently from active cooling or strike point sweeping. Extreme heat loads are predicted on future fusion reactor divertorsExpected engineering lifetime of plasma-facing components (PFC) loaded by 16 MW m −2 corresponds to an acceptable 3 months of cumulated plasma exposure (figure 18 in [1]), however, already for 25 MW m −2 it's only an hour (totally unacceptable). We predicted [2, 3] plasma heat flux q ⊥ perpendicular to the surface of divertor tiles (far off its edges) in ITER attached L-mode (without any fusion) as already q ⊥ =10 MW m −2 . Q=10 ITER H-mode yields P divertor ITER =(1-f rad )100 MW, ⅔ of which deposits on the outer target A dw =2πR 0 f x λ q,integral =0.4 m 2 area [4,42]. Properly controlled impurity seeding increases natural radiation fraction up to f rad =85% [5] on present tokamaks without undesired cooling of the fusing hot plasma core. Accounting further for the toroidal bevel, one gets q ⊥ =⅔P divertor ITER /A dw 4.2°/2.7°=31 MW m −2 [6], thus twice above the engineering limit.Assuming that rather the very complex and recent turbulence models XGC1 [7] and BOUT++ (figure 3 in [Xu19]) will be closer to reality than these empirical scalings, the energy will be deposited on a much more optimistic 5-10× larger area (λ q =6 mm thanks to stronger SOL turbulence due to larger a/r ion Larmor ), predicting thus 5<q ⊥ [MW m −2 ]<16 [1]. The European DEMO 2 GW fusion power plant study [8, 9] counts with similar P SOL =150 MW due to assumed strong core line radiation, namely to stay within the 16 MW m −2 limit, the DEMO edge+SOL+divertor radiation must never drop below 97% which is a big challenge. Estimate for the RECEIVED

No abstract