In Japan, the inport of LNG has been started in 1969, and immediately it will be enlarge as the new energy source. The problem of utilizing the cold from LNG vaporization has been examined, then it has been found out that the utilization cold for air separation plant is one of the most efficient process. This paper describes the fundametal problem of the air separation plant which utilizes the cold of LNG, and economics of the process.
Experiments are carried out to search a behavior of a flux jump under a control over the heat leakage from Nb-Ti rods surrounded by low pressure herium gas, and the following quantities are measured: the relation between the flux-jump field and the sweeping rate, the behavior of temperatre rise and temperature fluctuations. In order to compare with the experimental results, approximate solutions of a simplified heat equation to describe a flux jump and the induced mean power losses are derived for a cylindrical specimen in which the temperature is assumed to be constant spatially. Calculations are carried out for the several quantities concerned to flux jumps. In addition, an analysis of temperature fluctuations is worked under the condition of a least heat leakage, and the criteria of flux jumps are discussed.
To investigate the stability of the superconducting magnet placed in the changing magnetic field, some fundamental experiments have been carried out. The behaviors of the persistent current flowing in the superconducting closed circuit have been examined in the sinusoidally alternating magnetic field at fixed frequency of 50c/s, plus superimposed direct magnetic field. The amplitudes of the alternating magnetic field and direct magnetic field were varied from 0KG to 3.5KG and from 0KG to 10KG, respectively. The samples were Cu (0.14mm in the thickness) clad Nb-Ti wire (0.27mm in the diameter). Under the good cooling condition, after the persistent current decreased to a certain degree according to the applied magnetic fields, they became stable and didn't decay any more. The relations for the dependence of this stable persistent current on the applied magnetic fields have been derived by using the Bean's model for the magnetic field distribution in the superconductor. The measurements can be well explained by this relations. We will be able to predict the stable current flowing in the supercondctors placed in the changing magnetic field by considering the magnetic characteristics of the superconductors.
There are many types of persistent current switches for superconducting magnets, such as the one using the S-N transition of superconductors caused either thermally or magnetically, the one making and breaking mechanically, and so on. But, mechanical switches can be seen most feasible in them for the superconducting magnets wound by composite conductors with much normal metal substrates. In oder to adopt a mechanical persistent current switch to our saddle shaped superconducting magnet for 1kw MHD generator, we have tested several types of mechanical contact both in liquid nitrogen and in liquid helium, and then developed the mechanical switch which has the contact resistance below 0.1μΩ in liquid helium and current capacity above several hundred amperes. In this paper it is decribed how to decrease their contact resistance and how to impove them to operate stably in liquid helium. Then some design considerations are discussed to construct the switch with higher current capacity for the future superconducting magnet of larger scale.
The design process of a air-borne superconducting magnet for cosmic ray measurement is presented. The weight of all this magnet system must be less than 300kg and the magnetic field is 20kG with enough accesses for cosmic ray and for optical system. The superconducting magnet must work during 12 hours with persistent current mode. The construction of this magnet system is possible with a helium tank of 80l, utililzing the aluminum stabilized superconducting wire or the multiple filamentary superconducting wire.