Proposal of Hot-pressed, Rod-shaped Tungsten Armor Concept for ITER Divertor and its High-heat-flux Performances

Abstract

This paper describes the R&D of plasma facing components, especially the joining technology of the tungsten/copper joint for the ITER divertor application. The major concern for this joint is detachment due to the large differences in the thermal expansion coefficient and the modulus of elasticity of each metal. One solution is to separate the joint area into small pieces to reduce interfacial stress at the joint. From this viewpoint, JAERI proposes the hot-press method using small tungsten rods pressed into cylindrical bores in the copper substrate at high temperature. A divertor mock-up was fabricated to investigate the durability of this joint. No failures of the mock-up occurred in a thermal cycle experiment involving 3,000 cycles of 5 MW/m 2 heat flux. Using numerical analyses, the contact heat transfer coefficient between the tungsten and copper was determined to be 2,400 W/m 2 /K for this mock-up. Though this value is slightly inadequate to maintain the surface temperature below the recrystallization temperature of tungsten, it is significant that no embrittlement failures of the rod-shaped armor were observed. Further R&D is suggested to improve the hot-press method, including surface treatment of the rod faces or the use of insert material.

Temperature Distribution and Heat Flux on the EAST Divertor Targets in H-Mode

“…Handling the high-heat flux depositing on the divertor target plates is an important issue for future reactorsize fusion devices, especially for ITER [1] . According to the present ITER design, the peak power flux on the divertor plate would be around 20 MW/m 2 , which is too high compared with the tolerable engineering limit of 5 MW/m 2 [2] . The excessive heat loads on the divertor target plates can result in melting and evaporation which can severely influence the lifetime of divertor target plates and reduce discharge performance.…”

Pulsed Electric Current Bonding of Tungsten to Copper with Intermediate Layer

“…Copper alloys have been used as heat sink materials due to their high thermal conductivity. Tungsten and copper joints have been used for electrode components in plasma facing [1][2][3]. However, because of the distinctive differences in properties especially the melting point, W and Cu are usually difficult to weld.…”