This review article is concerned with the recent advances in the studies of the flux-line pinning. The fundamentals of the pinning mechanism are first explained briefly and next several methods to get a volume pinning force Fp caused by a random array of pins are described. The rigidity of the flux-line lattice is revealed to have important effects on the pinning characteristics. Two types of the flux-line motions are possible according to the lattice rigidity. The pinning force Fp is usually determined by the occurrence of a depinning flow, but sometimes in high magnetic fields it may be modified by the occurrence of a shearing flow. Pinning properties in high-field superconductors are also summarized and discussed. It is shown that in usual cases the pinning force Fp obeys the scaling law, i. e. Fp∞[Bc2(T)]mf(b), where Bc2 is the 2nd critical field and f(b) is a function of the reduced magnetic field b=B/Bc2 only. Finally, the effects of irradiations and stresses on the flux-line pinning are simply reviewed. The pinning properties of the compound superconductors are found to be more sensitive to irradiations and stresses than those of the alloy superconductors. It is mainly due to the high sensitivity of the critical temperatures to them in the compound superconductors.
The development of a large scale refrigeration system is being stimulated by new superconducting techniques representated by a superconducting power cable and a magnet. For the practical operation of such a large system, an automatic control system with a computer is required, because it can attain an effective and systematic operation. For this reason, we examined and developed micro-computer control techniques for supercritical He generation, as a simplified control model of the refrigeration system. The experimental results showed that the computer control system can attain fine controlability, even if the control element is only one magnetic valve, but a BASIK program language of micro-computer, which is convinient and generaly used, isn't enough one to control a more complicated system, because of its low calculating speed. Then we conclude that a more effective program language for micro-computer must be developed to realize practical refrigeration control.
New power supply for superconductor is proposed. The conventional power supply is consisted of a transformer and thyristors. The present power supply does not the large current transformer but only the switching devices to achieve the DC current amplification. The principle of new power supply is AC-DC-AC-DC conversion. The AC line is once rectified to small current of DC and next converted to large current of DC through switching device handling AC. On a test set, 800A of superconducting current has been obtained with 50A input DC current. The conceptual design of power supply for 20kA has been done. The characterisitc features of the new power supply have been compared with the conventional one.
It is wellknown that the gas oscillation appears in a tube whose one end is immersed in liquid He, and the other is closed at room temperature. A novel application of this oscillation is developed to increase the internal pressure in the He storage vessel. The apparatus includes a level meter to measure the liquid content, based on the same principle. Using the apparatus, the internal pressure can be controlled only by the valve operation. Moreover the liquid level can be measured even under the pressurized state.