Analysis of the NHMFL 45-T hybrid magnet thermal behavior

The superconducting outsert of the NHMFL 45-T is cooled by static He II contained in cable-in-conduit conductors, which must be capable of extracting any internal heat (primarily from hysteresis losses) during a ramp from zero to full field. In the event that the ramping losses exceed the cooling capacity of the He II, the long cooling channels become partially or completely filled by He I and even the relatively weak heating of index losses can lead to slow thermal runaway and a delayed quench. A numerical analysis is presented using a one-dimensional model of heat transfer in a column of superfluid helium. The model considers each of the six layers in the innermost coil as independent channels, yet coupled through heat transfer across conduit and insulation. The computational results are compared with experimental data, showing good agreement with the observed quench behavior. (C) 2003 Elsevier Science Ltd. All rights reserved.