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 (Lower 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 fabrication process and the grill can have a high mechanical strength at high temperature. A 24 x 4 multijunction grill, which consists of 24 waveguides and 4 waveguides in the toroidal and poloidal directions, respectively, has been successfully fabricated by this method and has demonstrated a power handling capability of up to 26 MW/m2 on JT-60U. Moreover, the diffusion bonding method can make a grill composed of two different kinds of material: one has a high thermal conductivity for the septum plates to remove RF (Radio Frequency) losses, and the other has a low electrical conductivity for the rods to reduce eddy currents during a plasma disruption. A test module composed of Dispersion Strengthened Copper and Stainless Steel has been fabricated and has shown the practical application of diffusion bonding in the fabrication of a LHCD grill for steady-state operation.