IN-SITU ANNEALING OF RADIATION DAMAGE OF OPTICAL COMPONENTS IN TOKAMAK DIAGNOSTICS

THE HARSH RADIATION ENVIRONMENT PRESENTED BY THE D-T BURNING PLASMA IN NEXT-STEP TOKAMAK FUSION DEVICES CAN CAUSE SEVERE DAMAGE TO CRITICAL OPTICAL COMPONENTS USED IN RESEARCH DIAGNOSTICS AND CONTROL INSTRUMENTATION. THE TECHNICAL OBJECTIVE OF PHASE I IS TO DETERMINE THE FEASIBILITY OF USING COMBINED THERMAL/OPTICAL ANNEALING TECHNIQUES TO MAINTAIN THE OPTICAL QUALITY OF THESE COMPONENTS. EXPERIMENTAL STUDIES, USING A TRIGA RESEARCH REACTOR TO SIMULATE THE RADIATION ENVIRONMENT EXPECTED IN FUSION DEVICES, WILL DETERMINE THE TECHNIQUES AND FREQUENCY REQUIRED TO CARRY OUT SUCH ANNEALING. THE GOAL IS TO FIND WAYS TO PERFORM ANNEALING REMOTELY WHILE THE FUSION DEVICE CONTINUES OPERATION. THIS WILL REQUIRE PERIODIC SHUT-DOWN OF DIAGNOSIS CHANNELS DURING ANNEALING. HOWEVER, BY USING A WELL-PLANNED SCHEDULE FOR THE ANNEALING AND INCORPORATING REDUNDANT CHANNELS WHERE REQUIRED THE BASIC DIAGNOSTICS NEEDED FOR SAFE OPERATION COULD BE MAINTAINED AT ALL TIMES. PHASE I WILL STUDY ANNEALING METHODS FOR REPRESENTATIVE SAMPLES OF SILICA AND ION MPLANTED CESIUM IODIDE. THESE TEST MATERIALS ARE SELECTED FOR RELATIVELY GOOD RESISTANCE TO RADIATION DAMAGE, BASED ON DATA FROM PAST STUDIES. THE EXPERIMENTAL PROGRAM WOULD THEN INVOLVE A TEST MATRIX, CONSISTING OF THE TWO SAMPLES, COMBINED WITH STUDIES OF THE THREE ANNEALING METHODS (THERMAL, OPTICAL, AND COMBINED), AND THREE DIFFERENT ANNEALING FREQUENCIES (I.E., THE INTERVAL BETWEEN ANNEALING). ISSUES TO BE RESOLVED INCLUDE THE OPTIMAL CONDITIONS (TEMPERATURES, LIGHT INTENSITIES ETC.) THE DURATION OF THE ANNEALING STEP, THE INTERVAL BETWEEN ANNE NG TREATMENTS NECESSARY TO MAINTAIN DESIRED TRANSMISSION LIMITS, AND THE EFFECTS OF REPEATED ANNEALING ON THE MATERIALS. IF THE FEASIBILITY OF THIS APPROACH IS ESTABLISHED IN PHASE I, STUDIES IN PHASE II WILL BE DESIGNED TO DEVELOP THE APPROPRIATE ANNEALING CAPABILITY FOR OPTICAL COMPONENTS IN SPECIFIC DIAGNOSTICS FOR NEXT-STEP FUSION DEVICES, SUCH AS THE INTERNATIONAL THERMONUCLEAR EXPERIMENTAL REACTOR AND THE SUBSEQUENT "DEMO" REACTOR.