The critical current in a NbTi tape measured in different directions of magnetic field and the current reduction due to the self field

With reference to the application of NbTi tape in a superconducting thermal switch, the critical current of a 20-¿m-thick NbTi tape was measured in several directions of the magnetic field. The critical current was found to behave strongly anisotropically, due to the deformation of the NbTi. The tape is extrasensitive to the component of the magnetic field perpendicular to the surface. Without an external field this component of the self-field reduces the critical current far below its intrinsic value. A one-dimensional model can describe the reduction of critical current due to the self-field in a thin tap

Quench development in superconducting cable having insulated strands with high resistive matrix: I. Experiment

The process of quench development in two- and six-strand cables was investigated in detail. Different types of quenches were found. The increase of the starting current level led to a change in the nature of the quench, from current redistribution, to a quench in all strands, to multi-quench with acceleration of the process from step to step, and to fast quench. Strand currents never achieved the critical current value under DC conditions. It is concluded that the cause of fast quench in AC cables is a specific mechanism of the electromagnetic development of quench. It is caused by a rapid redistribution of currents between the strands, which leads to a multi-quench process with acceleration of the normal zone propagation after each quench of the strand. The cause of the fast redistribution is the high inductive coupling coefficient between strands

Quench characteristics of a two-strand superconducting cable and the influence of its length

The quench process of a multi-strand cable was investigated using the simplest system: two twisted wires. Several properties of the quench, such as the commutation of currents, the time scale, the resistance rate, and the maximum voltage, were determined experimentally or by calculation. Particular attention was given to the role of the cable length. Several samples with lengths varying from 1.5 cm to 12 m were made from an AC superconductor with CuNi matrix. In the experiment, the decay of the currents was measured after initiating a local normal spot in one of the wires. An important conclusion is that the quench propagation and stability of a cable depend on its length and can therefore be influenced by soldering it at certain interval

Stability and quench development study in small HTSC magnet

Stability and quench development in a HTSC magnet have been experimentally studied with the transport current in the magnet being below or above the “thermal quench current” level. The magnet was tested at both cryocooler cooling and liquid nitrogen cooling, with and without background magnetic field (up to 4 T). The temperature and electrical voltages in different sections of the magnet were measured using 20 thermocouples and 24 potential taps embedded in the winding. In this paper, the experimental procedure and the results are described. The results are compared with those obtained earlier in the experiments with the smaller HTSC specimens and are analysed by using the scaling theory of the thermal quench