Normal-zone propagation properties in Bi-2223/Ag superconducting multifilament tapes

It is expected that the normal-zone propagation of a high-temperature superconductor (HTS) is slower than that of a low-temperature superconductor (LTS) because of its large heat capacity. If the normal-zone propagates too slowly, hot spots will develop, possibly resulting in permanent conductor damage. Accordingly, there is a need to measure propagation quantitatively for designing HTS magnets. This paper describes the electromagnetic and thermal behavior of Bi-2223/Ag superconducting multifilament tapes during normal transition by conduction cooling. Some experiments were carried out under the conditions of operating temperature at 10-40 K and transport current as parameters in a zero magnetic field. Sample tapes were transited normally with a heater to initiate a quench. The voltage and temperature properties corresponding to normal transition were measured by voltage taps and thermocouples attached to the sample tapes. We also calculated longitudinal and transverse-direction normal-zone propagation velocities from the voltage and temperature traces. In the case of conduction cooling, we investigated the cooling effect due to the length of the sample tape because its cooling condition is different from the case of using a coolant - for example, liquid helium.