The problems encountered in developing FRP cryostat have been solved and the FRP cryostat was successfully constructed. The FRP cryostats were confirmed to show the good performances and hence are thought to be applicable for various fields. In this paper the problems in constructing the cryostats were discussed and the methodology to solve the problems are suggested based on the experimental results. Finally the applicability of the cryostat was also discussed.
Recent advances in superconducting wire technology, together with economic advantage of superconducting magnets to produce high magnetic field, have stimulated increasing interest in large scale superconducting apparatus such as superconducting magnet energy storage in electric power systems, superconducting magnets for fusion reactors and superconducting power generators. Electrical insulations may become one of critical design factors because high voltages are produced by stringent energy discharge and quenching in large superconducting magnets. In this review, abnormal overvoltage, performance of coolant liquids under high electric field and dielectric performance of insulating components in superconducting apparatus are described.
Hysteresis losses in superconductors are caused by irreversible motion of fluxoids. This motion is in most cases described by the critical state model. In this report various electromagnetic phenomena due to flux pinning effect are reviewed and explanations on these phenomena are given by the critical state model. The phenomena which cannot be well described by the present model, such as reversible fluxoid motion and the longitudinal field effect, are also introduced.
A new purification system, operated at ambient temperature, has been developed. It purifies He to 99.999% and the recovery ratio of He is 99%. This system consists of PSA (Pressure Swing Adsorption), membrane, freon refrigerator, and compressor. The PSA purifier has adsorption tanks which contain activated carbon and synthesis zeolite. It can purify impure He gas which is contaminated with H2O, CO2, O2, Ar, and N2 to 99.999% He. The purge gas from PSA is circulated and recompressed to recover He, because the recovery ratio of He in PSA is only 75%. The membrane purifier consists of a module which contains many hollow fibers of cellulose acetate. This system can separate impure components (CO2, O2, Ar, N2) from He gas, which are condensed in the membrane, and exhausted. H2O is condensed in the freon refrigerator and exhausted. Then it is adsorbed by PSA to a concentration where the dew point is below -70°C. Because impure components are fully condensed in the membrane and the freon refrigerator, the recovery ratio of He in this system is therefore above 99%.
The feasibility of preparing YBaCuO films on metallic substrates was discussed in an attempt to fabricate a superconducting tape. Deposition method employed was an rf magnetron sputtering. MgO buffer layers were found to be a favorable choice to prevent the adverse reaction between the superconducting film and the underlying substrate. Particular attention was given to the preferential resputtering effect due to the bombardment of negative ions during sputtering. The substrate-cathode configuration used to achieve stoichiometric film composition was described. Highly oriented YBaCuO films have been obtained on a Hastelloy-X tape with a MgO buffer layer. The highest zero resistance temperature obtained so far of the YBaCuO thin films on a metallic tape was 80.4K in its as grown state, and a critical current density was 200A/cm2 at 77.4K and 104A/cm2 at 60K. Preliminary results of YBaCuO films deposited on a bundle of Chromel fine wires were also reported.
Heat transfer from horizontal surface to liquid helium II contained in a chamber connected to a bath through a channel have been measured. Temperature difference across the channel has been measured simultaneously. Ten kinds of channels having same void area were used. The effects of geometry of the channel cross section on heat transfer from solid surface to helium II and on heat transport in a channel were studied. In saturated helium II, the limiting heat flux defined as the beginning of film boiling on the heat transfer surface varies with the equivalent diameter of the channel. The maximum of the limiting heat flux is obtained at the equivalent diameter in the range of about 0.5 to 1.0mm. Temperature difference across the channel changed abruptly in high heat flux region and did not increased as ΔT∝q3 and heat transport was enhanced. In pressurized helium II, the limiting heat flux was unaffected by the equivalent diameter, and the values were nearly the same as the value obtained at the maximum of the limiting heat flux in saturated helium II.