Cooling liquid He-3 below 1 mK by nuclear demagnetization
Abstract
The design and construction of a nuclear adiabatic demagnetization cryostat is detailed and the cooling of approximately 20 cc of liquid He-3 to a temperature of 0.4 mK is discussed. The net heat leak to the nuclear stage was only 5 nW and the run time being 1 mK was in excess of two days. The thermal resistances between the liquid He-3 and the nuclear spins of the copper bundle are examined. Extensive calculations and measurements show that the Kapitza resistance between the palladium heat exchanger and the He-3 is the dominant factor. A single mathematical approach to optimizing the cooling of the He-3 by minimizing the entropy production in the bundle is also presented. The results of this optimization can be used with a microprocessor based controller to automate the demagnetization process and to evaluate the effects of making changes in the apparatus.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- December 1979
- Bibcode:
- 1979PhDT.......101M
- Keywords:
-
- Cryogenic Equipment;
- Cryogenics;
- Helium Isotopes;
- Cryostats;
- Demagnetization;
- Heat Exchangers;
- Kapitza Resistance;
- Relaxation Time;
- Spin-Lattice Relaxation;
- Engineering (General)