Stability of Nb3Sn superconducting wires: the role of the normal matrix

The stability of ���� superconducting wires is a crucial issue in the design and operation of reliable superconducting magnets. High current density magnets, such as those presently developed for future accelerator projects, may be subject to premature quenches due to local releases of energy. In this paper we study the results of stability experiments that have been performed using a single mode Diode Laser with an optical fiber to illuminate the superconducting strand surface and trigger fast quenches. The development and propagation of laser-induced quenches have been measured on Nb3Sn strands in LHe bath by means of three voltage taps. This paper deals with the numerical analysis of the experimental results. A coupled electric and thermal model has been developed to study the quench propagation. The experimental evidence of a different qualitative behavior of the voltage traces recorded on ���� strands with respect to NbTi strands is explained by means of a more detailed physical model of ���� strands, that takes into account electrical and thermal transverse resistances.