Test of a Prototype Nb₃Sn Sextupole Coil for 45-GHz ECR Ion Source Using Mirror Structure

Institute of Modern Physics is developing a Nb3Sn superconducting magnet system for a 45-GHz electron cyclotron resonance ion source. To achieve this complicated and challenging Nb3Sn magnet, a prototype with identical cross section but half the length of the magnet is proposed. A single sextupole coil prototype with 457 mm length has been fabricated and tested. This sextupole coil is 38 mm thick with an aperture of 200 mm. It was wound by using a 1.3-mm diameter Nb3Sn wire insulated with 0.11-mm-thick braided S-2 glass fiber. In order to test the coil in similar conditions than the magnet operation, a sextupole magnetic mirror structure is utilized. The bladder and key technology is employed to exert the required preload on the coil. This article describes the magnetic field design of the sextupole mirror structure, presents the fabrication of the sextupole coil, and reports the cryogenic test results.