Following an introduction of basic principles of a dilution refrigeration and a few comments on the nuclear demagnetization to produce ultra-low temperatures, a couple of methods to measure its temperature are described. As a typical example of quantum phenomena at ultra-low temperatures, some characteristic features of the superfluid 3He, nuclear ordered solid 3He, some properties of 3He-4He dilute solutions and enhanced nuclear magnetism are briefly described.
In every stage of experiment in low temperature physics and cryogenic engineering liquid helium and nitrogen are used popularly, but they are not necessarily used properly. The proper usage of these cryogen is reconsidered in this article by investigating the thermophysical property differences in latent heat, thermal conductivity, enthalpy and so on. To make your own cryogenic “map” based on thermophysical properties compared with other cryogen as hydrogen and oxygen would be the key to solve troubles encountered in your experiment.
Superconducting properties of Bi-Pb-Sr-Ca-Cu-O superconducting bulk fabricated by intermediate cold isostatic pressing (C. I. P.) process have been investigated, and heat leakage per a bulk lead pair from 77K to 4.2K has been evaluated. The critical current density of the tubular bulk, approximately inner diameter 10-30mm and 200mm long, was indicated more than 1, 000A/cm2 at 77K under self-magnetic field, and at 4.2K was indicated as about 2, 000A/cm2 under 15T. The reasons for improvement of Jc are the formation of high Tc single phase and highly aligned microstructure of the bulk. The heat leakage per a pair of the bulk leads from 77K to 4.2K has been measured to be 0.16W at DC 800A and considered to be less than one-tenth of that of 800A-class conventional gas-cooled current leads.