Design and thermal performance of an improved mechanically attached module for divertor plate of LHD

A mechanically attached divertor module with improved performance has been developed and partially installed in the large helical device (LHD). The advantage of the new design is to eliminate any metal bolts on the armor tile surface which leads to high Z impurity emission. The new module consists of a couple of armor tiles made of iso-graphite and a thin graphite sheet, which are tightened by two stainless steel (SS) or TZM bolts horizontally sandwiching a SS cooling pipe. The heat flows directly from the tile surface to the cooling pipe. The previous design used a copper heat sink has been used. Steady heat flux tests up to 1.2 MW/m2 have been carried out for the new module without any trouble using a electron gun ACT while the allowable heat flux of the previous module was limited below 0.3 MW/m2 due to deformation of the copper heat sink. The outgassing from the new module during heat flux tests up to 0.5 MW/m2 is decreased to about one-third. Thermal fatigue test up to 115 cycles under a steady heat flux of 1 MW/m2 for the new module has been performed without any troubles. Comparisons between the previous and new modules for the structure, thermal performance, and outgassing are made.