COMPOSITE MATERIALS WITH LOW Z, SELF-REGENERATING COATINGS FOR FUSION FIRST WALLS AND LIMITERS

THE CONDITIONS THAT PLASMA INTERACTIVE MATERIALS MUST FACE IN A MAGNETIC CONFINEMENT FUSION DEVICE ARE SUCH THAT THERE DOES NOT APPEAR TO BE ANY SINGLE MATERIAL THAT POSSESSES ALL THE NECESSARY PROPERTIES TO PREVENT EITHER CONTAMINATION OF THE PLASMA OR EARLY FAILURE OF THE PLASMA-SIDE COMPONENTS. CURRENTLY USED MATERIALS WILL NOT BE SATISFACTORY FOR LONG PULSE OR STEADY-STATE OPERATION. THE USE OF COATINGS HAS BEEN SUGGESTED AS A MEANS OF RESOLVING THE DIFFICULTY, BUT CONVENTIONAL COATINGS WILL NOT SURVIVE IN A REACTOR-GRADE PLASMA. SELF-REGENERATING MATERIALS OFFER A MEANS BY WHICH THE DIVERSE REQUIREMENTS OFA FUSION ENVIRONMENT MAY BE MET BY A SINGLE MATERIAL WITH A REASONABLE SERVICE LIFE. THESE MATERIALS DEPEND ON UTILIZING THE INTENSE THERMAL AND RADIATION FLUX OF THE FUSION ENVIRONMENT AS A MEANS OF PRODUCING A LOW-Z COATING THAT MINIMIZES PLASMA CONTAMINATION AND SELF-SPUTTERING AND AT THE SAME TIME IS RESISTANT TO LIGHT ION SPUTTERING. TERNARY COMPOSITE MATERIALS CONTAINING A REFRACTORY METAL, A GOOD THERMAL CONDUCTOR, AND AN ALKALI METAL ARE CAPABLE OFPROVIDING GOOD MELT-LAYER STABILITY AND BETTER SPUTTERING PROPERTIES THAN THOSE OBTAINABLE WITH ELEMENTAL MATERIALS OR ALLOYS.