Presentation Simulation Study of the Divertor Operation for a DEMO Fusion Reactor

Asakura, Nobuyuki  ,  Hoshino, Kazuo  ,  Homma, Yuuki  ,  Tokunaga, Shinsuke  ,  Joint Special Design Team for Fusion DEMO, the

Power handling in the divertor has been investigated for Japan DEMO concept. System code suggests the plasma line-av. ne (8.6x1019m-3~1.2nGW) lower than ITER. Plasma detachment in the low nesep (ne/3) = 2-3x1019m-3 has been investigated. Appropriate divertor size, i.e. larger than ITER-size leg, has been investigated. Divertor size will affect sizes of vacuum vessel, toroidal field coil and maintenance port as well as its cost. Divertor performance with leg length (Ldiv) of 1.6m was investigated in low SOL density (nesep = 1.5-2.4x10m-3), using SONIC with Ar seeding, Pout = 250MW (Psep= 235-240MW), high radiation fraction of 0.8 and fixed diffusion coefficients. High plasma temperature at SOL (Tesep = 300-600eV): local decay length of the parallel heat flux profile is 2.6-2.8 mm near the separatrix due to electron flux limiter, which is smaller than ITER simulation (3.6 mm, Tesep ~200 eV). Peak heat load at the dovertor target was reduced from 12 to ~5 MWm-2 with increasing separatrix density (nesep). nesep >2.2x1019m-3 was required to reduce Tediv to ~25 eV at the attached region of the outer target, and to reduce nAr/ne in SOL to ~0.5%. “Detachment plasma (~1eV)” was produced near the separatrix for both Ldiv = 1.1m and 1.6m cases, while higher Te and Ti at attached plasma area for the shorter case. Ar concentration in SOL was larger (~3%) for the short Ldiv = 1.1m case.
The 23rd International Conference on Plasma Surface Interactions in Controlled Fusion Devices (PSI-23)

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