Recent topics on the application of the low temperature techniques to polarized proton and deuteron targets are discussed. One of the important parts of the polarized target is its cryogenic system. For example, horizontal cryostats of He4 and He3 circulation system were constructed for the dynamic polarization of nuclei. The cooling power of cryostats are about 1W at 1°K or 20mW at 0.5°K. Furthermore dilution refrigerators with very high cooling power will be quite useful in near future. On the other hand, several types of superconducting magnets were designed for polarized targets. Magnetic field of 25-50kG with the homogeneity of the order of 10-4 in the volume of about 100-500cm3 and large angular apertures for scattering of high energy particles are required.
Measurements on magnetic properties in a bulk Pb-In-Sn alloy superconductor were carried out. H-I characteristics in the superconducting wire were also measured. In a certain range of temperature and magnetic field, magnetizations of the bulk sample or critical current densities of the wire one increased with increasing temperature, i.e., the superconductor exhibited the property ∂Jc/∂T>0. In the regoins where ∂Jc /∂T is positive or negative, flux jumping characteristics, the effects of magnetic field sweep on magnetizations, current-voltage behaviours and so on were measured. In the positive region, intrinsically stable behaviour was confirmed; no flux jumps were observed, magnetizations increased by a certain value with field sweep rates and the voltage was reversible up to fairly large current over its critical current. While in the negative region. flux jumps occurred.
MHD power generators have been investigated in the Electrotechnical Laboratory as one of National Research and Development programs. A turbo-expander has been developed for a part of the helium refrigerator to cool the super-conducting magnet for the MHD power generator. The turbo-expander uses externally pressurized gas bearings of low temperature helium to operate the system at a low temperature. An alternator of 4.0kW is employed for the brake of the turbo-expander. The outside diameter of turbine is 40mm and the diameter of rotor with magnets is 30mm. The turbo-expander can be rotated smoothly up to the speed of 120, 000rpm at low temperature when the gas pressure of bearing is 11ata and the flow rate is less than 28m3/hr. The output power of the turbine is 1.3kW when the outlet temperature and pressure are 9.5°K and 0.53ata, respectively. A big liquener of 2001/hr has been designed utilizing the turbo-expanders. The liquefier will be used for the MHD power generator of 1, 000kW.