Elastic buckling of superconducting Yin-Yang magnets for fusion

A small superconducting model of yin-yang coils for the Mirror Fusion Test Facility has exhibited a magnetoelastic buckling instability. The 1:22 model, wound with 150 turns of niobium titanium wire and potted in epoxy, can carry up to 30 10³Amp-turns. Rotational motion of the magnets is observed to increase as the current approaches a critical value, while the torsional natural frequency is observed to decrease with current. A prediction of the buckling current based on a theoretical model is found to be higher than the measured values. The phenomenon is similar to that observed for tokamak toroidal field magnets. Structural design implications for Yin-Yang magnets are discussed.