In this paper, we reviewed the current progress of superconducting devices, specially High Tc three terminal devices. Properties of High Tc material and developments of the process technology are briefly summarized. A superconducting base three terminal device of In/(Ba, Rb) BiO3/SrTiO3(Nb) structure was procuced and evaluated. With a base thickness of 70nm, α=0.94 and β=10 were achieved. High Tc field effect transistors and flux-flow transistors, which have been operated in a good transistor action, are reviewed.
The viscosity of liquid 4He has been measured by means of a high-Q torsional oscillator at temperatures between 1.5K and 2.7K under saturated vapor pressure. The viscosity data derived from the resonant frequency difference between the empty cell and the cell filled with liquid 4He show satisfactory agreement with the results obtained by Welber. When the velocity of cell-wall exceeded the critical velocity below the superfluid transition temperature, the decrease of the resonant frequency caused by the growth of the quantized-vortex was observed. In the case of a cell with rough wall, the critical velocity was low compared with a cell with smooth wall. The rate of the growth of vortex line length also depends on the wall roughness.
A forced-cooled superconducting coil has been studied for the next step fusion machines because of many merits. The coil can be cooled by supercritical helium below 4.5K, which improves the stability and other superconducting characteristics. To study the stability of the coil at lower temperature, a test coil wound in a one-layer solenoid with a CIC conductor was tested below 4.5K. It was proved that the stability at lower temperature would be able to predict from the relationship between the critical current below 4.5K and the stability characteristics at 4.5K. The limiting current at lower temperature is in good agreement with the Lottin's experimental results.