A superconducting magnet spectrometer was launched up to an altitude of 36.5km by using a large bolloon-borne in order to observe high energy cosmic rays and to search for primordial antimatter in the Universe. The first balloon-borne experiment was successfully carried out in Northern Canada in summer of 1993. Development of the superconducting magnet spectrometer and progress of the baloon-borne experiment are described in this report.
This paper presents an overview of the superconductive magnetically levitated system (maglev) program in the United States. Although the U.S. Maglev Program was once stopped in 1975, the increasing congestion in the U.S. transportation system in the late 1980's and other factors have led to a reawakening of national interest in Maglev technology. In 1990 the National Maglev Initiative (NMI) was established, and it funded 27 studies related to Maglev technologies and economics, and four System Concept Definition (SCD) studies. Technical requirements in the SCD and technologies in the SCD systems designed by teams led by Bechtel Corp., Foster-Miller Inc., Grumman Aerospace Corp. and Magneplane International, Inc. will be reviewed. A plan for the Maglev prototype development program proposed in the NMI program will be also presented.
As YBCO oxide superconductor has high critical temperature and high critical magnetic field, a great deal of research has been conducted due to great potential applications. The evaluation of the mechanical property of YBCO system is therefore important in addition to superconducting properties. However such studies are few, and the fracture mechanism of YBCO has not been investigated. In this paper, the Brazilian test and cyclic loading tests were performed in liquid nitrogen to evaluate the microfracture behavior of YBCO superconductor by use of SQUID (Superconducting QUantum Interference Devices). Initiation and extension of cracks can be detected by use of SQUID as variation in the magnetic field caused by cracks under applied current. The sign of SQUID signal indicates the cracking location, because the sign depends on the location of cracks and sensing coil of SQUID.
The present authors have succeeded in optical observation on thermal disturbance, quench zone, and its rapid propagation in a superconducting coil, immersion-cooled in liquid helium, by producing the respective dark zones corresponding to them on its illuminated surface. The thermal disturbance to the test coil was applied by pulse-heating of film heaters wound in it. Transient behavior of the dark zones under various conditions of pulse heating and transport current was recorded with a high-speed video system, and compared with the measured time histories of tap voltages and temperatures at various locations of the test coil; the agreement was very good. Fundamental study by experiments using a pulse-heated strip of stainless steel film revealed the following: The optical observation is possible when the wall heat flux of the test piece is greater than 140W/m2 and its wall superheat is greater than 0.3K. In such a case, a light beam is scattered in a very thin thermal layer at the liquid-solid interface and luminous energy of reflected light from the interface is attenuated. With increasing pulse-heat flux, the reflected luminous energy decreases drastically and initiation time of the attenuation is shortened.
In multiply-twisted superconducting cables in a transverse external magnetic field, the strands of multifilamentary wires are exposed to a spatially periodic field component longitudinal to the strand axis. It is predicted theoretically in 50/60Hz region that the AC loss of the wires for the longitudinal component is not neglected or comparable with that for a pure transverse field in the multiply-twisted cables with cabling pitches of several cm and more. In the present paper, the AC loss in the spatially periodic longitudinal field was experimentally evaluated by means of measuring electromagnetically the AC loss of short multifilamentary wires in a 60Hz uniform longitudinal one. It results from a theoretical consideration that the above two types of losses are equivalent to each other within errors of 5%, where the sample length corresponds to a half of the wavelength of the field. The measured loss was quantitatively explained by the theoretical expression for spatially periodic longitudinal field above mentioned. These results suggest that the AC loss in the cables for AC use should be minimized under consideration of the longitudinal loss in addition to the usual transverse losses.
On the development of the superconducting poloidal coil, it is important to examine the mechanical behavior and the compressive rigidity of the coil at liquid helium temperature. The superconducting poloidal coils are subjected to the compressive stress of about 20-35MPa. This paper deals with the displacement and strain analysis of the superconducting poloidal coil pack under compressive load at liquid helium temperature. Finite element method is used for the numerical analysis of the composite structure of the coil pack. The numerical results of displacements and strains are obtained and compared with the experimental results. The validity of numerical analysis for evaluating the rigidity of the coil pack is also discussed.
The positron annihilation method has been used to evaluate the unoccupied space of epoxies aiming at the molecular design of epoxy for cryogenic use. The fracture toughness of the commercially available epoxies was measured and was compared with the life time τ3. The epoxy was found to be classified into two types that is (i) those shows the increase of fracture toughness with free volume and (ii) those do not present large change with increasing free volume evaluated by positron annihilation. The former was understood as the system with disordered network and the latterr as that with different crosslinking density. The discussion suggests that the latter system is preferable for cryogenic use and was confirmed experimentally.