JT-60SU divertor conceptual design

General Atomics recently completed a divertor design study for JAERI for th e JT-60 Super Upgrade (JT-60SU) tokamak. JT-60SU is being designed as a sup erconducting device for an integrated R&D investigation of steady-state ope ration in a tokamak. A divertor design was developed to accommodate double- null operation for a 1000 s discharge duration at 8 MA of plasma current an d 80 MW of auxiliary heating. The work reported here is an extension of a p revious design study.(1,2) The thermal requirements are a peak heat flux of 9 MW/m(2), a maximum surface temperature of 1600 degreesC, and a poloidal cooling flow configuration for the plasma facing components. The structural requirements are determined from both the predicted stresses due to halo c urrents as well as the stresses due to differential thermal expansion encou ntered during bakeout. The halo current loads are based on a nominal halo c urrent of 0.19 Ip with a 2.0 toroidal peaking factor. Analysis has determin ed that the halo current load per centimeter of circumference is P = 2856 ( 1+cos theta) N/cm, where 8 is the toroidal angle. The loads due to differen tial thermal expansion are a result of an expected 100 degreesC temperature difference between the vacuum vessel and divertor during bakeout. Based on the aforementioned criteria, a divertor design was developed for a ll three areas of the JT-60SU divertor: the inner baffle, the private flux baffle, and the outer baffle. In order to have highly reliable divertor com ponents, flexible supports sized to accommodate the structural loads are ut ilized in the design rather than insulators or sliding interfaces. The plas ma facing components are mounted on a structural mounting plate to form a r emovable and remotely-maintainable segment which is in turn mounted on the supports. For outer and private flux baffles, these structural mounting pla tes are joined together using a double shear joint design to form a structu rally continuous ring to react the halo current loads. The plasma facing co mponents are broken into 80 segmentation; however, the outer and private fl ux baffles have an alternating 8 degrees and 16 degrees structural segmenta tion which forms the double shear toroidal structural joint. The inner baff le takes advantage of its relatively short poloidal length and its proximit y to the vacuum vessel to provide structural integrity. The thermal design consists of a plasma facing material of flat CFC tiles that are brazed onto a poloidally cooled copper heat sink. Adequate gaps between the baffles an d wall are provided for pumping of recycled gas.