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The long term reliability of the SMES model coil for the 100 kWh SMES pilot plant was investigated in a 1000 cycles cyclic test in the test facility of the Lawrence Livermore National Laboratory (LLNL) in 1998, in collaboration between Japan and the USA. The coil parameters such as coil inductance, magnetic field and AC loss were measured before and after the cyclic test. They did not change. The coil was successfully charged up to 40.53 kA in the mechanical performance test, which gave mechanically the same conditions as in the SMES pilot plant at rated current. After all performance tests, the coil was checked visually and electrically, and no degradation was observed. Mechanical reliability of the SMES model coil was verified in the performance tests. The obtained technical results encourage recommendation of the construction of the pilot plant.

The stray field of SMES restricts its site location, although SMES has an attractive potential for power management and quality control. The stray field outside a solenoid is analyzed by a series of Legendre polynomials and the result is applied to the stray fields of various SMES coil configurations. As long as the summation of magnetic moments from all coils is zero, the term of a stray field decreasing as r/sub p//sup -3/ can be cancelled out. The higher order of the stray field can vanish if the coil arrangement is optimized. In this paper, the authors consider a single solenoid as a reference, active shield coils, axially displaced coils and multipole coils to reduce the stray field. The multipole coil configuration has high potential to drop the stray field, since the stray field behaves like r/sub p//sup (3+n/2)/, where n is the coil number.

Superconducting conductors and magnets used in the fields of power transmission, generators, MRI, MAGLEV etc. experience AC magnetic fields causing heat generation in the magnets' structure and AC losses in the superconductors. Therefore, AC magnetic shields with wide frequency range in high magnetic fields are desirable to reduce heat generation within the cryogenic region and increase system efficiency. This paper describes the performance of a multilayer superconducting sheet as an AC magnetic field shield, eddy current analysis of MAGLEV coil and eddy current loss measurement of an R&D cryostat with a superconducting magnet. Eddy current loss was reduced to about one fourth of the loss level without a superconducting shield.

Stability margin of the cable-in-conduit conductor is greatly influenced by current transfer performance among strands. When we estimate the stability margin analytically, we must assume the electrical circuit model among strands, but it is difficult to know it for real-scale cables, because the cable has many parallel circuits with a lot of strands and twisted stages. The measurement of the frequency characteristics of impedance among strands shows that the circuit can be regarded as two-wire model. By this measurement we can judge whether the circuit behaves like a distributed constant circuit or a lumped element circuit within the intended frequency band. When the circuit is a lumped element circuit, we can also get the interval distance between each contact point and its resistance. This paper also shows that stable conductors are often represented with a lumped element circuit that has well-contacted points with a short interval.

The transverse resistance among strands of multi-stage twisted cables is one of the most important parameters to decide the stability and the AC losses. This value is varied with the cable compression affected by the void fraction or the Lorentz forces under charging. Furthermore it is also influenced by cyclic number of transversal compression. This paper describes the basic mechanical property of the chrome plated NbTi cable for the transverse compression, and the relation of the transverse resistance and the internal loads of the cable by measuring the impedance and the rigidity for various internal loads. It shows that the transverse resistance, which is much influenced with the performance of conductor, is always changed corresponding to the compressive load and dose not indicate the same resistance after release from the compression because of its elastic hysteresis.

Dry-wound superconducting solenoids offer good manufacturability of large bore magnets but occasionally suffer from premature quenches triggered by small heat generated within the magnets. The principal source of heat is thought to be conductor motion induced frictional heating and/or filler material fracture released energy in windings. This paper describes major specification, stress analysis and training performance and their relation to a series of magnets that were constructed and tested to establish stabilizing methods of a large bore dry-wound superconducting solenoid. The results suggested that conductor motion took place even though radial stress in the magnet was still compressive and a conductor was expected in its original position. >

The stability margin of CIC multi-strand superconducting cables under partial current distribution is affected by electrical resistance among the strands. This means that the stability is governed by the current sharing process among the strands. The achievement of high stability against partial current distribution will be realized by rapid current transfer to the other strands rather than by thermal diffusion of Joule heating to helium. A simplified electrical circuit model, that is a distributed constant circuit for two strands, simulating the current sharing process between strands, is proposed to estimate the stability. The results of the stability analysis, clarify the limiting condition to maintain stability. The circuit constants governing the sharing process can be investigated from the frequency properties of a characteristic impedance measured with CICC short samples. These results are confirmed with experimental results of stability tests under partial current distribution. The proposed estimation method is viable. >