S. Masuzaki

T. Morisaki

Y. Kubota

National Institute for Fusion Science (NIFS-Repository)

§1. R&D of Surface-Boltless Mechanically Attached Divertor Plate for LHD Kubota, Y., Masuzaki, S., Morisaki, T. A surface-boltless mechanically attached divenor plate (SBLOP) has been developed and applied to LHO in the seventh campaign as a standing type instead of nonnal mechanically attached divenor plates (NMAOP). Comparison of the structure and thennal performance between the two types of divenor plates has been done. About 1,700 NMAOPs have been installed in LHO since the third campaign, each of which consists of a bTfaphite armor tile, a copper heat sink, a stainless steel(SS) back plate, and nonnal graphite sheets to improve thermal transfer, which are tightly fixed with eight SS bolts sandwiching a SS cooling pipe. They worked without any trouble till the fifth campaign. However, during long pulse plasma experiment in the sixth campaign by ICRH, a remarkable temperature increase and hot spots were observed on the graphite armor tile of the standing type of NMAOP. An increase in the temperature of divenor plate leads to a great deal of gas desorption. Moreover, partially melted tracks caused by a dense plasma irradiation were observed on the SS bolt heads used to fix the annor tile, which may be an origin of high Z impurity in core plasma. To achieve successfully long pulse plasma experiment as an important mission of LHD, the large improvement of thennal perfonnance of helical divertor plates and boltless structure on armor tile surface are strongly required. Therefore, SBLOP without any bolt on the tilc surface and a copper heat sink which leads to the poor thennal performance has been developed and evaluated using a test facility ACT with a 100kW electron gun. The cross-sectional view of SBLOP is shown in Fig. I. The divertor plate consists of a couple of graphite annor tiles and super graphite sheet, which are tightly fixed horizontally with two TZM(or SS) bolts sandwiching the cooling pipe. Electron beams • t? Graphite armor tiles TZM M6 bolts SS bar nut SS cooling pipe Super graphite sheet Fig.l Cross-sectional view of surface boltless mechanically attached divertor plate for LHO. 90 The annor tile material is iso-graphite(1G-430U) with a thermal conductivity of 139W/mK similar to that of NMAOP. However, the super graphite sheet(PGS-IOO) has very excellent thennal and mechanical properties different trom the normal graphite sheet(PF-20UHP) used in the NMAOP. The disassembled structure ofSBLOP is compared with that of NMAOP in Fig.2. The simple structure of SBLOP allows to reduce the number of bolts used for fix to 114, the total weight by 40%, and the setting time to half compared to the previous one. Fig.2 A comparison of the structures between two types. The left is SBLOP and the right is NMAOP. The thermal performance and outgassing of the SBLOP have been evaluated comparing with those ofNMAOP using a test facility ACT. High heat flux tests up to 1.2 MW/m2 for steady state operation have been carried out, and the relationship between the temperature and heat flux is shown in Fig.3. The figure indicates that the allowable heat flux of SBLOP exceeds 1.0 MW/m' although that of NMAOP is limited to the low value, about 0.3 MW/m2 By changing SS bolts(Red line) to TZM bolts(Black line), which are used to fix the armor tiles, the thennal performance is more improved. The gas amount desorbed from SBLOP during high heat flux tests from 0.1 to 0.5 MW/m'is much reduced, less than one-third of that ofNMAOP. Temperature dependency on heat flux for two types of divertor plates '"00 "--""-f A)NMJ P , n wlIhN S / '00 r----I---{''TT'''.+-'=F'7."' .E .. ! • "k/~~-F~---l r: ,~:_~_-r/h ('~.+--o ___ <i'. .. .. I I Bl S LDP Ts n Til T. Th Th '-, Fig.3 Relationship between the applied heat flux and measured temperarures. TS,Tu, and Th are temperatures at the tile surface, tile bottom, and heat sink, respectively. 

R&D of Surface-Boltless Mechanically Attached Divertor Plate for LHD

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