Quench energy and fatigue degradation properties of Cu- and Al/Cu-stabilized Nb-Ti epoxy-impregnated superconductor coils

In comparative measurements of small-scale epoxy-impregnated Cu-stabilized and Al/Cu-stabilized Nb-Ti test coils at 4 K and 5 T, the heat energy required to quench the Al/Cu-stabilized coil was 4 to 12 times greater than for the Cu-stabilized coil, depending on the relative operating current. Also, the coils' stabilizer resistivity (/spl rho/) was measured as a function of mechanical fatigue to test for strain-induced degradation. The /spl rho/ of the Cu-stabilized coil is relatively unaffected by fatigue, while that of the Al/Cu-stabilized coil increases with fatigue. However, in these coils, having a typical stabilizer:superconductor ratio of 4:1, the degradation of the Al/Cu-stabilized coil begins to saturate after several hundred fatigue cycles; after 2000 fatigue cycles to 0.2% strain, the /spl rho/ of the Al/Cu-stabilized coil is still 2.6 times lower than the /spl rho/ of the Cu-stabilized coil. Furthermore, after annealing the Al/Cu-stabilized coil at room temperature for 48 hours, the /spl rho/ degradation was reduced by 76%. Thus, the use of Al/Cu stabilizer may offer substantial improvements in magnet stability, even where the magnet is subjected to fatigue degradation from repeatedly energizing the magnet.<
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