Principles of advanced quench detection design in cable-in-conduit (CICC) magnets

The design and development of novel quench detection systems for the International Thermonuclear Experimental Reactor (ITER) and the Tokamak Physics Experiment (TPX) has advanced our knowledge of design principles governing quench detection systems. Design studies have quantified the detection signal-noise ratios for several types of quench detector, including external and cowound voltage sensors, fiber optic temperature sensors, and optical and piezoresistive flow meters. The effects of sensor placement and subdivision have also been studied. Sensor topologies with the highest signal-noise ratios are identified. Fiber-optic and voltage sensors have been fabricated for the ITER QUELL experiment, that have demonstrated the capacity to survive cabling and compaction, heat treatment, and cooldown to low temperature with tight conduit bend radii. Extraction techniques have been developed that use redundant seals and coefficient-of-expansion matching to guarantee leak-tightness. Electrical integrity is guaranteed in a design through the control of electrical fields in the feedthrough geometry and insulation material selection.