Thermal Phase Transitions in Superconducting Nb-Zr Alloys

Abstract

Experimental data are presented for the thermal propagation of a normal-superconducting boundary along wires of Nb-25%Zr, Nb-37%Zr, and Nb-51%Zr. The thermal propagation velocity was measured as a function of current at 4.2°K in constant longitudinal and transverse magnetic fields up to the upper critical field Hc2 as well as in a zero magnetic field for temperatures between 2.5° and 11°K. Previous models which describe thermal propagation phenomena neglected the temperature dependences of the specific heat, thermal conductivity, and electrical resistivity. A more exact model is proposed here which takes into account the temperature dependences of these quantities, and all the present experimental data are in good agreement with this model. From a measurement at 4.2°K of the dependence of the thermal velocity on magnetic field, the high-field transition temperatures as a function of magnetic field are calculated for temperatures above 4.2°K. In conjunction with the theory, the linear dependence of the thermal velocity on current implies a weak current dependence for both the transition temperature and superconducting-state specific heat in Nb-Zr alloys up to 3×105 A/cm2. A method is discussed for using thermal propagation techniques to determine the superconducting-state specific heat in the presence of known transport currents and magnetic fields.

Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part II: Model predictions and comparison with experimental results

“…This equation is non linear, so that simplifying hypotheses had to be made to get an analytical solution or, at least, an estimation of v q . The first assumption in [7][8][9] is that the whole conductor can be represented as a superconducting (SC) region adjacent to a normal conducting region, with different material properties. The transition occurs at temperature T tr , called transition temperature, corresponding to the boundary between these regions, for which travelling coordinate z ¼ 0 is assumed.…”

“…These analytical models assume a monodimensional cable geometry, describing the cable as a solid homogeneous material cooled by a helium bath with constant temperature or in adiabatic conditions [7][8][9]. The temperature profile along the conductor is supposed to propagate as a wave travelling at the quench propagation velocity v q without modifying its shape.…”

The measurement and theoretical calculation of quench velocities within large fully epoxy impregnated superconducting coils

“…The theory applies to insulated wires for which the amount of heat conducted radially away from the wire can be neglected' [2,4]. The effect of current sharing between the matrix material (copper) and superconductor is included [3][4].…”

“…It is used to predict some quench velocities, which are then compared with experimental data [1][2][3][4].…”

Variation of Quench Propagation Velocities in YBCO Cables

“…Naturally, when modelling quench evolution in superconducting magnets using NZPV based methods, knowing NZPV with enough accuracy in longitudinal and transverse directions is crucial. The methods to gather NZPV data are either experimental [8,9,11] or computational [12][13][14][15][16][17].…”