The development of a magnetic levitation system in Japan was launched in 1962. After about thirty years' R & D, in 1990, a test line in Yamanashi prefecture was authorized as a national funded project in Japan. R & D entered a new phase. This paper describes the necessity of the Chuo Shinkansen which is expected to adopt the superconducting magnetic levitation system, the outline of the project, and the present status of developing the technology.
A vacuum technique is one of the most important techniques in cryogenics. The thermal insulation (MLI) and the production of superfluid helium are the main applications of the vacuum techniques. The calculations of vacuum conductances, pumping speed and ultimate pressure including a low temperature case are explained. The vacuum components (pumps, tubings, valves, flanges, gauges) within a vacuum system are also explained. Especially the techniques to maintain the clean vacuum of the thermal insulation are described in detail. The vacuum leak test is also important for making a good cryostat.
The thermal diffusivity (α) and the conductivity (κ) of Bi-2223 sintered material was measured between 12 and 200K under an identical experimental setup using a closed cycle helium refrigerator. The electronic contribution to the thermal conductivity was calculated by Wiedemann-Franz law above the critical temperature (Tc) and by Kadanoff's expression below Tc, respectively. The electronic component was substracted from the total thermal conductivity in order to derive the phonon thermal conductivity. The phonon thermal conductivity was analyzed using the theory by Tewordt & Wölkhausen. The contributions of phonons to α were separated out by use of the simultaneously obtained κ data.
Thermal conductivity of Dy3Ga5O12 garnet single crystal has been measured between 2 and 20K with various magnetic fields between 0 and 5T. We have found a large magnetic field dependence of the thermal conductivity (λ); λ decreases with the magnetic field from 0 to 1T and then increases slightly above 1.5T. The maximum reduction in λ is found at 3.5K and 1.5T. The value is -70 times smaller than that at 3.5K and 0T. The experimental result shows that Dy3Ga5O12 single crystal has the thermal switch function controlled by the magnetic field between 0 and 1.5T in the temperature between 2 and 10K. The large magnetic field dependence of λ can be explained by the resonant type phonon scattering corresponding to the phonon-induced transition between the energy levels of rate earth ions which are modified by the magnetic field.