LOW-TEMPERATURE THERMAL-PROPERTIES OF COMPOSITE INSULATION SYSTEMS

The thermal contraction and thermal conductivity of candidate composite insulation systems for the International Thermonuclear Experimental Reactor toroidal field coils were measured from 295 to 4 K. Matrix materials consisted of a diglycidyl ether of bisphenol-A epoxy suitable for vacuum impregnation, a tetrafunctional epoxy suitable for pre-impregnation, a polyimide system produced by a high-pressure laminating process, and a bismaleimide system. These matrix materials were combined with S-2 glass fabric and various barrier systems, such as ceramic and organic coatings, polyimide film and mica/glass. Thermal contraction was measured by the strain gauge method in which strain gauges are attached directly to the specimen. The thermal contraction in the through-thickness direction was different at 4 K for each resin system and changed slightly with the addition of electrical barriers. The thermal conductivity of the materials, with and without the electrical barriers, was similar at 4 K, but more distinctive at higher temperatures. The systems with the ceramic coatings exhibited the highest thermal conductivities at all temperatures.