Steady-State Heat Transfer in He II through Porous Superconducting Cable Insulation

Abstract

The LHC program includes the study of thermal behavior of the superconducting cables wound in the dipole magnet cooled by superfluid helium (He II). Insulation of these superconducting cables forms the major thermal shield hindering the He II cooling. This is particularly a problem in magnets which are subjected to thermal loads. To investigate He II heat transfer processes an experimental model has been realized which creates a one-dimensional heat transfer in such media. Insulation is generally realized by wrapping around the superconducting cable a combination of different kind of Kapton^® tapes, fiber-glass impregnated by epoxy resin or Kevlar^® fiber tapes. Steady-state heat transfer in He II through these multi-layer porous slabs has been analyzed. Experimental results for a range of heat flux show the existence of different thermal regimes related to He II. It is shown that the parameters of importance are a global geometrical factor which could be considered as an equivalent “permeability” related to He II heat transfer, the transfer function f(T) of He II and the thermal conductivity of the slab. We present and analyze results for different insulations as a function of the temperature.