부산대학교 도서관

Plasma facing components in fusion devices such as tokamaks must often sustain heat fluxes in the 2 to 40 MW/m{sup 2} range. In this environment, it is essential that armor tiles be affixed to an actively cooled substrate with a minimum of thermal contact resistance. For divertor plates, limiters, beam dumps, and other high-heat-flux components used in fusion devices, low Z armor tiles, such as graphite, or high Z armor tiles, such as tungsten, are often brazed to cooled, highly conductive substrates, such as copper. The brazes that are typically 2 to 3 mils thick are chosen for certain characteristics, including (a) the ability to wet the materials to be joined, (b) braze time and temperature and consequent effects on material properties, and (c) metallurgical considerations, such as the potential formation of intermetallic alloys. The effect, or lack of effect, that the braze filler metal has on the granular structure of the metal substrate (copper) is also a consideration. Brazes will be needed in experimental fusion reactors in order to fasten armor tiles to substrates with minimal thermal contact resistance. Calculations of the activation products formed when candidate brazes are irradiated rule out the use of those containing significant amounts of silver or palladium according to current low-level-waste disposal limits. Some of the brazes that are most promising from a waste-disposal perspective have rather small engineering data bases on which to predicate their performance and may have less advantageous metallurgical characteristics. Investigations are continuing to identify promising armor tile-braze-substrate combinations. 3 refs., 1 tab.