Influence of Longitudinal and Transverse Components of External Magnetic Field on Current Distribution and Thermo-Magnetic Instabilities in Multifilamentary Superconductors

Abstract

In complicated magnet systems such as ones for fusion plasma experiments, or in multiplyt-wisted AC superconducting cables, multifilamentary composite superconductors are exposed to the external magnetic field with longitudinal component that is parallel to the conductor axis as well as transverse component. The transverse magnetic field makes the current distribution in the conductor uniform. The longitudinal magnetic field also influences the current distribution in the conductor. The cross section of conductors generally consists of the saturated region where filaments carry their critical current and the non-saturated region. The magnetic flux enclosed by one pitch of the electrical center lines of two adjacent filaments with the same azimuthal angle should be zero in the non-saturated region. With this condition, the current distribution in multifilamentary superconductors that carry the trasnport current and are exposed to the external magnetic field with both the longitudinal and transverse components is calculated. The thickness of the saturated region at the stability limit against thermo-magnetic instabilities is calculated to evaluate the transport current at the stability limit. The longitudinal magnetic field is possible to make the saturated region thicker, and to degrade the transport current at the stability limit. Increasing filament diameter and/or magnitude of transverse magnetic field increase the transport current at the stability limit, because they make the current distribution uniform and decrease the thickness of the saturated region. Increasing critical current density and conductor radius decrease the ratio of the transport current at the stability limit to the critical current. Quench current degradation due to thermo-magnetic instabilities induced by the longitudinal magnetic field should be taken into considerations when we design superconductors for complicated magnet systems.