Numerical Analysis on Dynamic One-side Propagation of Normal Zone Observed in LHD Conductor

Abstract

The dynamic one‐side propagation of a normal zone, which was initiated by a thermal disturbance, was observed in the superconducting helical coils of the Large Helical Device (LHD). The initiated normal zone propagated only to one‐side along the conductor, and shrank after a few seconds. The dynamic one‐side propagation phenomenon was not expected during the design stage of the LHD, and it has not been explained yet. In this paper, a new numerical code is proposed for predicting the dynamic one‐side propagation phenomenon. As a result of the transient stability simulation, the asymmetrical propagation of a normal zone was seen. At the early stage of the current distribution, symmetrically circulating Hall currents flowed to the longitudinal direction with respect to the center of the initiated normal zone. These Hall currents cause the asymmetrical Joule heat distribution, with the result that the asymmetrical propagation is generated. This is the first time that the dynamic one‐side propagation phenomenon was simulated successfully. The asymmetrical propagation is attributed to the asymmetrical design of the conductor cross‐section and the use of the stabilizing materials with different sign of the Hall coefficient.