X-ray imaging diagnostics, and tomographic imagingsystems in particular, are on the official list of requireddiagnostics for the International Thermonuclear ExperimentalReactor (ITER) tokamak. They will provide crucial informationabout magnetohydrodynamic fluctuations, and sense precursors todisruptive instabilities, that must be monitored and avoided inmachine operation. In addition, they will be utilized fordetermining plasma position and shape, for measuring radiativepower during normal tokamak operation, and for other specialpurposes (such as monitoring impurity transport) during thephysics-study phases of burning-plasma tokamak projects such asITER and the Tokamak Physics Experiment. Conventional techniquesapplied to xray imaging diagnostics on existing tokamaks will notwork for burning-plasma tokamaks such as ITER. These techniquesinvolve system components (typically solid-state detectors) thatwill fail when exposed to the large neutron fluxes thatcharacterize the harsh environments in which they must work. Thisproject will develop a conceptual design for a practical,radiation-hardened, tomographic x-ray imaging system forburning-plasma tokamaks such as ITER. The design will be based ona detector type which is intrinsically immune to radiationdamage. In Phase I, a proof-of-principle study will be performed,and a novel type of vacuum photodiode detector, which holds greatpromise for this application, will be optimized. The optimizeddetector would form part of a complete system, to be designed inPhase II, which would address issues of diagnostic 56 access,spatial resolution, temporal resolution, and sensitivity.Anticipated Results/Potential Commercial Applications as described by the awardee:This project will produce novelapproaches to the design of a crucial type of diagnostic(tomographic x-ray imaging) for burning-plasma tokamaks. Apractical design for such an instrument must be developed for theadvanced tokamaks now being designed for demonstratingproof-of-principle of fusion power.
