AN IMPROVED HEAVY ION BEAM DETECTOR FOR PLASMA SYSTEMS

PARTICLE BEAMS ARE COMMONLY USED FOR PLASMA DIAGNOSTICS TO OBTAIN TIME AND SPATIALLY RESOLVED MEASUREMENTS OF DENSITY, TEMPERATURE, AND SPACE CHARGE POTENTIAL. AN IMPORTANT APPLICATION IS IN CONTROLLED FUSION RESEARCH WHERE FLUCTUATIONS IN THESE QUANTITITES ARE KNOWN TO HAVE AN IMPORTANT EFFECT ON ADEQUATE CONFINEMENT OF THE THERMONUCLEAR PLASMA TO REALIZE NET POWER OUTPUT. DURING THE LAST FEW YEARS, BEAM PROBE MEASUREMENT ON EXPERIMENTS SUCH AS THE ORIGINAL TEXAS EXPERIMENTAL TOKAMAK (TEXT) HAVE CONCENTRATED ON THE CHARACTERIZATION OF THE INTERIOR FLUCTUATIONS, AND LARGE DISCREPANCIES STILL EXIST BETWEEN THEORETICAL PREDICTIONS AND EXPERIMENTAL MEASUREMENTS BY A VARIETY OF TECHNIQUES. THERE IS, THEREFORE, A NEED FOR MORE DEFINITIVE EXPERIMENTAL MEASUREMENTS. TO DATE, ONLY TWO-POINT CORRELATION TECHNIQUES HAVE BEEN USED ON THE BEAM PROBE DATA. THE RESULT IS THAT ONLY THE MEAN WAVE-NUMBER, K, AND THE SPECTRAL WIDTH, SIGMA K, OF THE TURBULENCE DISTRIBUTION, S(K,W), CAN BE DETERMINED; NO INFORMATION CAN BE EXTRACTED ON OTHER FEATURES OF THE SPECTRUM. BY EXTENDING THE RANGE AND NUMBER OF SAMPLE VOLUMES SIMULTANEOUSLY RECORDES, A BETTER UNDERSTANDING OF THE LOW-K TURBULENCE MEASURED BY THE BEAM PROBE CAN BE ACHIEVED. THIS CAN BE ACCOMPLISHED BY PLACING AN ARRAY OF BEAM DETECTORS NEAR THE PLASMA EDGE. HOWEVER, TO OBTAIN THE ACCURACY REQUIRED FOR DENSITY FLUCTUATIONS IN TOKAMAK EXPERIMENTS, THE DETECTORS MUST BE SENSITIVE TO 0.1% OR BETTER IN THE HARSH ENVIRONMENT NEAR THE PLASMA EDGE. THESE MEASUREMENTS WILL PROVIDE A BETTER UNDERSTANDING OF TOKAMAK PLASMA EQUILIBRIUM, STABILITY, AND TRANSPORT. PHASE I WILL BE A FEASIBILITY AND OPTIMIZATION DESIGN STUDY FOR A HIGH-ENERGY ION BEAM DETECTOR THAT CAN PROVIDE THIS ACCURACY.