Numerical Analysis of Transient Transverse Hall Current in LHD Conductor

For aluminum-stabilized large conductors used in fusion magnets and other devices, it is essential to consider not only steady-state stability but also transient stability. In the helical coils of the Large Helical Device (LHD) of the National Institute for Fusion Science (NIFS), transient stability was not considered when designing the conductors; as a result, they quenched before reaching the rated excitation. Although the delay in current sharing with the aluminum stabilizer after the normal transition is regarded to be one of the responsible factors, it is unable to explain the transient excessive heat generation. The effect of Hall current loops generated in the conductor cross section has been noted; however, no detailed transient simulation has been performed so far. In this study, a transient simulation code that incorporates the Hall coefficient into the two-dimensional Finite Difference Time Domain (FDTD) method was developed, and the process of transport current redistribution in the stabilizer and the growth of Hall current loops in the conductor cross-section was simulated. The calculated steady-state effective resistance of the LHD conductor at 7 T agrees with the measured values, successfully explaining the anomalous magnetoresistance caused by the Hall current.