Research work on the magnetic confinement of plasma which forms the basis of fusion power generation, has recently made considerable progress and one expects that the scientific feasibility of fusion power reactor might be demonstrated towards the early date of 1980's. Aside from the gigantic superconducting magnet system for future fusion reactor, we have made a survey of the actual superconducting magnet systems for the plasma confinement in the various laboratories, and described these systems, dividing them into 3 categories, that is, open (magnetic mirror) type, internal ring type and toroidal magnet type. In these systems some of the internal ring type have been successfully operated and produced good results. Others are not yet so fruitful in plasma experiments but they are also supplying the creative data for the promotion of both the superconducting magnets and the plasma confinement technology. Our present applications of superconductor in this field is very limited as compared with those of other countries. As the superconducting magnet system will hold the very important role in the fusion power reactor, we should now start the long term program for superconducting magnet technology to cope with the requirements of the plasma confinement.
A systematic study has been carried out for Nb-Ti wires to investigate the effects of neutron irradiation on Jc's of Nb-Ti wires with a variety of metallurgical structures. The samples used in the present study are Nb-47.8at%Ti (named #A) and Nb-59.8at%Ti (named #B), which are aged at 380°C for 0-104min and irradiated up to 1.3×1018n/cm2 (En>0.1MeV). The Jc's of #A and of #B aged up to 50min are increased by the irradiation. But the Jc's of #B aged longer than 100min are decreased. In these longer aged samples of #B, the presence of Ti enriched precipitates such as alpha and omega phase is estimated from the data of Tc. The Tc's of #A and of #B aged up to 100min are changed little by the irradiation, but the decrease of Tc is observed in #B aged longer than 500min. This decrease indicates that the Ti concentration in the matrix may be increased in terms of radiation induced breakup of the precipitates, and thus causes the reduction in Jc by the irradiation. It is concluded that the superconducting Nb-Ti wire with precipitation enhanced Jc does not appear very resistant to neutron irradiation. Careful consideratiion should be, therefore, stressed in the choice of superconducting wire in its application to fusion reactor magnets.
A low power tunnel diode oscillator with high frequency stability, which operates at liquid helium temperatures is reported. The stability of the oscillating frequency is affected not only by the current flowing in the diode, but also the stability of temperatures of the circuit. Many attempts to stabilize the frequency are discussed here. One of the results of the density of He3-He4 mixtures (15% He3-He4), measured by this circuit, is also reported.