Comparing the thermal stability of NbTi and Nb₃Sn wires

Abstract

The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb 3 Sn wires in pool boiling Helium I. A comparison of the quench behavior of two typical NbTi and Nb 3 Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb 3 Sn wires are reported and analyzed. It is shown that the Nb 3 Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operation current and pulse duration and magnetic field. It is shown that the Nb 3 Sn wire exhibits a 'kink' of the quench energy vs current curve that makes the quench energy of Nb 3 Sn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic-thermal model, with special emphasis on the detailed description of heat exchange with liquid helium. AbstractThe investigation of quenching in low temperature superconducting wires is of

Performance analysis of the Nb−Ti conductor qualification samples for the ITER project

“…Another important parameter for the assessment of the conductor performance is the minimum quench energy (MQE). Numerous experimental tests and numerical analyses of this parameter have been performed in the past both on individual strands [18,19] and cable in conduit conductors [20][21][22][23]. Selected results of the MQE tests performed on the Nb-Ti CPQS conductors of the ITER Project are reported here, showing the dependence of the MQE on the temperature margin with respect to the current sharing temperature of each conductor.…”

Effect of Strand Damage in Nb3Sn Rutherford Cables on the Quench Propagation in Accelerator Magnets

“…For the high current densities that are present in the saturated strands the time constants may be too short for this assumption to be valid. It has been noted on the past that treating the strand elements in a homogenized way may not be accurate in certain strand stability regimes [9,23]. The copper in-between the embedded Nb3Sn filaments may have to be modelled as separate entity from the rest of the copper.…”

Quench and stability of Roebel cables at 77 K and self-field: Minimum quench power, cold end cooling, and cable cooling efficiency

“…Additionally, we allowed for current sharing rather than a sharp transition to fully normal state assumes an sharp transition from nucleate to film boiling while in reality a mixed boiling regime will exist across the temperature gradient and a more advanced analysis similar to that performed by Breschi et al for LHe will provide a more realistic picture near this discrepancy [30].…”