Species-Selective Pressure Gauge for High Performance Divertors

The Species-Selective Penning Gauge is used in fusion reactors to measure helium and tritium concentrations. However, when used in certain situations, such as in high performance divertors, the optical emission signals saturate when the pressure becomes too high. The use of differential pumping is not only an undesirable solution in tritium applications; it is also unacceptable in plasma processing due to high effluent reprocessing costs. This project will attempt to overcome the saturation limit by investigating changes in geometry, cathode material, anode potential, and/or magnetic field of the Penning gauge tube. Once an effective combination of changes is determined, a commercially feasible device will be developed and tested. In Phase I, all feasible changes to the Penning tube parameters (or combinations thereof) were tried and tested under different hydrogen/helium concentrations. An operational regime was found that allows non-saturated operation for at least one order of magnitude 'above the present (-5mTorr) limit. In Phase II,the newly found operational mode will be developed into a commercially sound prototype. With the prototype diagnostic at hand, the new limits for fusion applications will be explored and the compatibility with plasma processing applications will be examined. Commercial Applications and Other Benefits as described by the awardee: The enhanced species-selective gauge should be substantially less costly and more robust than a mass spectrometer. In industrial applications, it should be cost effective to use the gauge in large .numbers, not only for process control but also for pollution control by monitoring all possible effluents.