Design and Test of a Superconducting Undulator Mock-Up Coil at SSRF

A 0.88 T Nb-Ti superconducting undulator with a period length of 16 mm and a period number of 50 is proposed recently at SSRF. The magnetic field simulation shows that it is possible to obtain a peak field of 0.88 T on the beam axis at a magnetic gap of 8 mm. And two coil formers of five periods have been machined from SAE1018 stainless steel and sputtered with thin TiO₂ film for insulation. One coil former has been wound with copper wires and impregnated with epoxy resins, and the other has been wound using Nb-Ti/Cu wires, impregnated and tested. The dimension of the grooves of the coil windings is 5 mm × 12 mm. Formvar insulated Nb-Ti/Cu superconducting wires with a diameter of 0.6 mm are used to wind the coils. Experimental results show that the critical current of the coil could reach as high as 312 A at 2.5 T, 88% of the critical current of short Nb-Ti/Cu samples from the same bunch, which means the coil winding and impregnation crafts employed could meet the requirement of the 0.88 T Nb-Ti superconducting undulator.