Heat transfer and stability characteristics of cable bundles in He I and subcooled He II

Abstract

Results from two experiments aimed at understanding the stability of cabled composite superconductors are reported. The first is a heat transfer study of stainless steel tubular bundles. The peak heat flux from these test sections is investigated as a function of number of bundle tubes and gap between each tube. Experiments are performed in both He I at 4.2 K and subcooled He II at approximately 2 K. Results indicate that the peak heat flux is supressed substantially as the gap between tubes is reduced. With zero gap the surface averaged heat flux is only about 20% of that achieved with large gaps roughly equivalent to an open bath. The second experiment consists of a stability measurement on a bundled composite conductor. The test section is made up of a 66.3 cm length of a 7 wire bundle. The six outer wires are copper-NbTi composites while the core is an insulated resistance wire. Normalization of the conductor, either achieved by exceeding I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> or by pulsing the heater, is detected by voltage taps across the inductively wound test section. Stability measurements made in both He I and He II are correlated with the heat transfer results in the first experiment.