Systematic Study of Micro-stability of Superconducting Magnets

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9.1 Micro-stability of Tightly-wound Superconducting MagnetsIn order to recognize of the adaptable regime of the stability theory (Paper No.1), two non-impregnated coils with a winding inside diameter of 90 mm were made as parameters of copper-superconductor ratios. Their quench and heated tests were carried out, and their winding current densities and limited disturbances were measured.The coefficient of thermal expansion of a GFRP former was measured. Stability of the magnets will be analyzed by the use of this datum and strains measured by the coil tests.9.2 Micro-stability of CICC MagnetsThe practical design criterion for CICC magnets (Paper No.4) was applied to three pairs of poloidal coils for the Large Helical Device (LHD) of NIFS.The lower Inner Vertical (IV-L) Coil (Papers No.5 and No.6) was successfully tested up to the rated current of 20.8 kA without a quench. It is considered that the design criterion is reasonable and no-insulation on the conductor surface is good for stability.Short samples of CICC for LHD and two-stranded samples were tested to research current-distribution instability of CICC,and limited disturbance densities were measured.9.3 Micro-stability of Cryogenic MagnetsAnalysis of limited disturbance densities were carried out for cryogenic magnets. The equivalent current of disturbance was proposed for a stability criterion.9.4 Scaling Law for Superconducting MagnetsThe stored energy dependence of winding current densities of many superconducting magnets were investigated and the scaling laws were obtained empirically and theoretically.