A. Kurumada

N. Noda

T. Oku

Y. Imamura

Y. Tomota

National Institute for Fusion Science (NIFS-Repository)

§ 7. Development and Temperature Controlof Ceramics DivertorsTomota, Y., Kurumada, A., Imamura, Y. (Faculty ofEngineering, Ibaraki Univ.), Oku, T. (The Univ. ofthe Air), Noda, N.Ceramics (SiC/SiC composite, B4C and others) areexpected to use as a divertor for the LHD during continuousoperation, long time and steady state discharges because ofthe high heat resistance and the excellent nuclear properties.In this study, divertor model specimens made of SiC/SiCcomposite materials were manufactured as one of theplasma facing components having high performances.And the integrity of the divertor model specimens wastested by a deflection-type electron beam heating apparatus.The SiC/SiC composite material tested in this study wasmade by the polymer infiltration process (pIP) using them-NICALON SiC fiber.Eight pieces of the SiC/SiC composite (20x2.5x5 mm)were joined with an oxygen free copper block (20x20x20mm) having a cooling pipe (7 mm in inner diameter, 10 mmin outer diameter and 70 mm in length) after polishing andacetone washing. In the joining, titanium (0.05 mm inthickness) and copper (0.01 mm in thickness) foils wereused, and a molybdenum plate (0.5 mm in thickness) wasinserted for a relaxation of thermal stresses. The joiningspecimens were held for 30 minutes at 1000 degrees C in avacuum of IxIO·s Torr. [1,2]Heat fluxes from 0.5 to 5 MW/m2, that the one cycle wasIO-sec irradiation and IS-sec interval, were irradiated to thedivertor model specimens by the deflection-type electronbeam heating apparatus. The water coolant speed was 15Vmin at 15 degrees C. Before and after the heat load tests,the microstructures of the joining parts were observed bySEM.By insert of molybdenum, thermal cracks weren'tobserved at the joining parts and the shear strengths of thejoining interfaces increased. So the good joint of theSiC/SiC composite divertor model specimen wasconfirmed.Fig. 1 shows the SiC/SiC composite divertor modelspecimen after heat load tests. The surface temperature ofthe SiC/SiC composite material increased abruptly withincreasing heat flux, the surface eroded remarkably and thepieces ofthe SiC/SiC composite material delaminated at thejoining interface. On the other hand, the lowertemperature of the joining part rose little. One of thereasons was considered that the heat didn't transfersufficiently because of the low thermal conductivity anddelamination cracks.Consequently, the JOInIng process of the SiC/SiCcomposite materials was established, however, the SiC/SiCcomposite material was necessary to be improved thethermal conductivity and the resistance to erosion as thenext step task. These results were useful knowledge forthe development of the ceramics divertor having highperformances.Fig. 1. SiC/SiC composite divertor model specimenafter heat load tests.Reference[1] Imamura, Y, Oku, T., Kurumada, A, Tomota, Y, et al.,Proceedings of 1999 US-Japan Workshop (99FT-OS), NewMexico, USA, (1999.11.1-4), VIII 23-27.[2] Kurumada, A, Imamura, Y, Tomota, Y, Oku, T., et al., 1.ofNuclear Materials, 313-316 (2003) 245-249.83

Development and Temperature Control of Ceramics Divertors

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