Development of direct HIP-bonding processes for tungsten-brush armor joining

This paper reviews the design, fabrication, and high-heat-flux testing of tungsten-armored mockups for advanced divertor applications that require active cooling. These mockups represent a single cooling channel, limited length section of a typical element of the divertor plate. They employ the tungsten-brush armor form that has demonstrated acceptable performance at 25 MW/m/sup 2/ absorbed heat flux, surviving over 500 cycles at this level in previous testing at Sandia National Laboratories. The mockups discussed here represent the first attempt to adapt the direct-bonding approach to a HIP (Hot-Isostatic-Press) process, which enables brush-armor bonding over large areas with compound-curvature surfaces. The direct-bonding approach eliminates the application of a plasma-sprayed copper matrix over the bundled brush elements and the associated clean-up machining prior to bonding. Simple, modular fabrication was a key design driver for these mockups since advanced divertor modules must be affordable yet satisfy demanding performance and remote maintenance requirements. The mockups demonstrated successful armor joining using the direct-HIP process, but final high-heat flux testing was limited due to difficulties with melting of the honeycomb layer used to fixture the tungsten rods during fabrication. The paper discusses lessons-learned on these parts and concepts for eliminating the honeycomb on future mockups.