ADVANCED LOW-STRESS BRAZING OF PLASMA-FACING FUSION COMPONENTS WITH HIGH ENERGY ELECTRON BEAMS

THE USE OF HIGH ENERGY (E ~ 2 TO 19 MEV) ELECTRON BEAMS (HEEB) AT HIGH AVERAGE POWER (P ~ 50 KW TO 1 MW) ALLOWS COMPRESSION ANNEALED PYROLYTIC GRAPHITE (CAPG) AND CARBON-CARBON (CC) COMPOSITE COMPONENTS TO BE JOINED TO METALLIC SUBSTRATES WITHOUT THE HIGH RESIDUAL STRESSES THAT ACCOMPANY CONVENTIONAL BRAZING. RELIABLE BRAZING OF CAPG AND CC TO COPPER ALLOYS IS NECESSARY TO FABRICATE PLASMA LIMITERS AND DIVERTERS FOR USE IN A NEXT LARGE FUSION REACTOR. HEEB JOINING UTILIZES DEEP-PENETRATION VOLUMETRIC HEATING TO PREFERENTIALLY MELT A THIN, HIGH-Z BRAZE ALLOY INTERLAYER. THE LOCALIZED POWER DEPOSITION RAISES THE GRAPHITE AND INTERLAYER TEMPERATURES WITHOUT HEATING OF THE METALLIC SUBSTRATE. THE PROCESS ELIMINATES THE SUBSTRATE COOLING STEP AND THE RESIDUAL STRESSES AND BRAZE FAILURES CAUSED BY THERMAL EXPANSION MISMATCH. HEEB BRAZING WITH INDUCTION LINACS IS A HIGH-THROUGHPUT PROCESS, WHICH WILL ALLOW FABRICATION OF A DIVERTER COMPOSED OF HUNDREDS OF THOUSANDS OF TILES AT LOW UNIT COST. A NEW GENERATION OF PULSED INDUCTION LINEAR ACCELERATORS HAS BEEN DEVELOPED WHICH ALLOW RELIABLE, COST EFFICIENT PRODUCTION OF HIGH AVERAGE POWER ELECTRON BEAMS WITH THE NECESSARY PARAMETERS FOR CARBON BRAZING. A UNIQUE FEATURE OF THESE ACCELERATORS IS THE HIGH REPETITION RATE (>5000 PPS) ALL-SOLID-STATE PULSED POWER DRIVERS WHICH MAKE THESE ACCELERATORS SCALABLE TO MW POWER LEVELS AT AN ELECTRON MEAM COST OF $2 TO 3/WATT. THE INDUCTION ACCELERATOR TECHNOLOGY IS CONSISTENT WITH THE POWER DENSITIES (1 TO 5 KW/CM(2) ) AND BEAM ENERGIES (2 TO 10 MEV) REQUIRED FOR LOW-STRESS BRAZING. PRELIMINARY EXPERIMENTS IN PHASE I WILL DEMONSTRATE LOW-STRESS JOINING AND DETERMINE JOINT PROPERTIES. PROCESS OPTIMIZATION AND THE FABRICATION OF GRAPHITE AND CC FIRST-WALL LIMITER PROTOTYPES ARE PLANNED FOR PHASE II.