A (He-3)-gap heat switch for use below 2 K in zero g

We have designed and tested a compact heat switch that has a simple design and a very large ON/OFF ratio. The design uses concentric cylinders of copper that can be fabricated with higher precision and with thinner web thickness than other designs. It is assembled with a technique that carefully controls the narrow gap between adjacent segments. These features allow a very large surface area for conduction to be fitted into a small volume. The conduction medium is liquid or gaseous He-3, which is put into or taken out of the switch by a small nearby charcoal pump in order to avoid an external mechanical pump and a long pump line. Measurements of its performance down to 1 K show an ON/OFF conduction ratio of about 4000.