Premature quenches of thin coil under tangential tension by external magnetic field

An investigation of the tangential tension of a thin coil under the effect of an external magnetic field has been carried out. The test coil consists of a strong stainless steel bobbin, an epoxy impregnated winding (four layers of Nb-Ti wire of 0.85-mm diameter), and a stainless steel band. The winding diameter is 650 mm, and the height is 18 mm. The winding has two double-layer sections which can be energized independently. The coil has been tested under an external magnetic field up to 4.3 T. The equivalent stress reached 1050 MPa. Radial displacements of the winding were measured as function of coil current under several magnetic fields. The anisotropy of displacements for different radial directions was observed. Dependencies of quench currents on magnetic field were obtained for different modes of energizing the coil sections. Quench currents reach the critical current of the short sample if the mean radial strain is about 0.01%. The degradation of the coil is connected with large values of radial deformation. The limiting strain which forces the quench is about 0.13% for energizing of the coil with the band present. After reeling off the band, the utmost strain increased up to 0.22%