Thermomechanical modeling has indicated the desirability of using "brush-like" structures (clusters of small filaments or rods) for armor in plasma facing components as a means of reducing thermal stresses at the joint with the heat sink. Prior fabrication approaches for brush-like structures have discouraged the use of this armor configuration for large-scale applications. Development work in the US under ITER and DOE Small Business Innovative Research (SBIR) efforts, as well as in-house development at Plasma Processes, Inc., have resulted in potential methods for fabricating tungsten (W) brush structures suitable for application over areas the size of the ITER vertical target and dome surfaces.

Methods under development use 1.6-mm and 3.2-mm-diameter tungsten welding electrodes as stock for the armor and welded metallic honeycomb for fixturing during application of the copper backing matrix. Cu or Cu/W functionally-graded materials (FGMs) are plasma sprayed to the rear surface of the fixtured W electrodes. This provides a suitable interface for bonding to the Cu-alloy heat sink using low temperature (below 550^oC) Cu/Cu diffusion bonding techniques also being developed in the US under ITER funding. The honeycomb core may be left in place to provide transpiration cooling (using a lower melting point material such as aluminum) or as an indication of armor wear once it appears as a plasma impurity.

This brush armor concept will require a large number of tungsten rods (> 107) for the ITER dome and vertical target production application. Concepts and plans for cost-effective scale-up and large-scale component fabrication will be discussed. Additionally, the results of testing to determine honeycomb material and optimum processing parameters will be presented.

* Work supported by US DOE through SBIR grant and Contract AC3013 with Sandia National Laboratories