On propagation of plane fronts of normal zone within superconducting winding of magnet

Normal zone propagation within superconducting winding is studied theoretically in the model of discrete structure with alternating layers of superconductor and insulation. The exact solutions for longitudinal and transverse propagation, in steady regime, are obtained under assumptions that material parameters do not depend on temperature. For low current density j the general expressions for longitudinal v_|| and transverse v_⊥ velocities coincide with known result (v_||, v_⊥~j) in continuum approximation. Noticeable deviations from this linear dependence occur at high enough current density (v_⊥~j^2/3), when the heating time of metal is much less or of order of the time of transverse thermal diffusion through insulating layer. In dimensionless units, the dependencies v_||(j) and v_⊥(j) are described by universal curves for a given ratio of specific heat of superconductor and insulation