A description is given of refrigerators in which the superfluid 4He is entering through superleak. These are, for example, the vortex pump refrigerator and the 4He-circulating dilution refrigerator. Although these are rather different type refrigerators, the superfluidity of 4He plays an essential role for their cooling principles and operations. The view point of superleak-operation will make it much clear.
Recently the research and development on the super-conducting power transmission cable and communication cable have been continued. To control these systems, it is important to know an open loop characteristic function of the whole system. In this paper, the characteristic function pertaining to a practical cooling system model has been derived by solving directly the partial derivative equations of fluid dynamics.
This report describes the stability of superconducting coils wound with fine multi-filamentary wires and impregnated with Wood's metal. The training effect and current degradation observed before impregnation are remarkably improved after impregnation. The instability of superconductin coils seems to originate in “wire movement” in the winding. In comparison with organic impregnants, low melting point-metals such as Wood's metal are effective impregnants in suppressing “wire movement” in the winding and in elevating the stability of superconductin coils, because cracks and voids do not exist in the winding owing to good osmosis in the melting state and coils are well cooled owing to good thermal conductivity.
The influence of oscillating magnetic fields on the DC transport current in a single core superconducting wire has been studied by observing the terminal voltage of the wire. The voltage versus oscillating field characteristics can be explained quantitatively by a theoretical analysis based on the critical state model. The analysis shows that the voltage measurement gives detailed information on the change of the distribution of the magnetic induction inside the superconductor. An effective resistance appears in the transport current loop when the amplitude of the oscillating field exceeds a certain threshold value. The dependence of the effective resistance on the amplitude and frequency of the oscillating field and on the conductor diameter is discussed.
The control of fluids in cryogenic plants requires valves which are specially designed to operate at cryogenic temperature. The problems mentioned include structure, heat inleak, materials pressure-drop and comments on the practice of application, insulation etc.