Monitoring of superconducting bus-line of LHD using fuzzy theorem

In the LHD (Large-scale Helical Device) system of National Institute for Fu sion Science (NIFS), Toki, Gifu, Japan, the experiments using superconducti ng magnets with total stored energy of roughly 1.6GJ are carried out. The L HD consists of nine coils those are fed by large-scale DC power supply. The superconducting bus-lines ape connecting the power supply and coils with a length of about 50m and a current capacity of 32kA (rated current). As thi s bus-Line has thick stabilizing backing metal thigh purity A)), a resistiv e voltage generated at small normal-transitioned region is very small. Mean while, the inductive voltage noise induced by the external magnetic field o r its own magnetic field is large because the length of the bus-line is lar ge. Besides, the voltage detection leads cannot be attached directly just o utside the conductors because of the thick thermal insulation and the care for electrical insulation. Therefore, it is difficult to decide the state o f the superconducting bus-line only by the voltage signals. So, the authors proposed to introduce the Fuzzy theorem calculating the "dangerous rate" o f the bus-line. In this system, not only the voltage signals of the bus-lin e but also the transport current and the liquid helium flow-rate in the bus -line are taken into consideration. The experimental result shows that the state of the bus-lines is well expressed by the "dangerous rate", and the b us-lime has enough operation margin.