DEVELOPMENT OF A DIFFUSION BONDING METHOD FOR FABRICATION OF LOWER-HYBRID CURRENT DRIVE GRILLS

A diffusion bonding method has been developed to fabricate a LHCD (Low er Hybrid Current Drive) grill with a large number of waveguides. The grill is composed of several thin septum plates and pairs of rods, and is constructed by diffusion bonding. This method simplifies the fabri cation process and the grill can have a high mechanical strength at hi gh temperature. A 24 x 4 multijunction grill, which consists of 24 wav eguides and 4 waveguides in the toroidal and poloidal directions, resp ectively, has been successfully fabricated by this method and has demo nstrated a power handling capability of up to 26 MW/m2 on JT-60U. More over, the diffusion bonding method can make a grill composed of two di fferent kinds of material: one has a high thermal conductivity for the septum plates to remove RF (Radio Frequency) losses, and the other ha s a low electrical conductivity for the rods to reduce eddy currents d uring a plasma disruption. A test module composed of Dispersion Streng thened Copper and Stainless Steel has been fabricated and has shown th e practical application of diffusion bonding in the fabrication of a L HCD grill for steady-state operation.