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Heat transfer characteristics of the first wall with graphite sheet interlayer

Masaki, Kei; Miyo, Yasuhiko; Sakurai, Shinji; Ezato, Koichiro; Suzuki, Satoshi; Sakasai, Akira

Steady-state research is indispensable to establish scientific and technological basis for the next fusion devices. In JT-60, long pulse operation of up to 65s (OH) with a neutral beam heating power of $$sim$$12 MW (30s) was conducted to investigate the plasma behavior in several tens of seconds. However, the structure of the JT-60U first wall, which was composed of bolted graphite tiles and backings, restricted the flexibility of the plasma operation, because the first wall was not actively cooled. To improve the heat transfer characteristics of the first wall taking into account the cost, a candidate is to insert a graphite sheet between the graphite tile and the backing plate. Aiming at a design study for next fusion devices, the heat transfer characteristics of the first wall structure were investigated with a variety of graphite sheets and fixing-bolt torque conditions. The first wall mockup used for the experiment was composed of three CFC tiles (125(L) $$times$$110(W)$$times$$24(T) mm for each tile) and a cupper-alloy heat sink (377(L)$$times$$100(W)$$times$$20(T) mm) with two cooling channels of 10 mm diameter. Four types of the graphite sheets, 0.1-mm thickness PGS (Pyrolytic Graphite Sheet; Panasoic Co., Ltd), 0.2-mm PF (Perma Foil; Toyo Tanso Co., Ltd) 0.38-mm PF, 0.6-mm PF, were examined in the experiment. The heat load tests of the mockup were performed with the heat fluxes of 1 and 3 MW/m$$^{2}$$ on the JAERI electron beam irradiation stand. The experimental results showed that the structure with 0.1-mm thickness $$times$$ 3 PGSs had the highest heat transfer performance in the experiment. The first wall structure with the PGS sheets withstood the heat flux of 1 MW/m$$^{2}$$$$times$$100s. The maximum surface temperature of the CFC tile was 500$$^{circ}$$C. Furthermore, the results indicated that the structure could be used at the steady-state condition with the heat flux of $$sim$$1 MW/m$$^{2}$$. In the paper, detail of the results will be presented and discussed.

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