A Nb3Sn superconducting coil can be formed from a wire including multiple unreacted strands comprising tin in contact with niobium. The strands are wound into a cable, which is then heated to react the tin and niobium to form a cable comprising reacted Nb3Sn strands. The cable comprising the reacted Nb3Sn strands are then mounted in and soldered into an electrically conductive channel to form a reacted cable-in-channel of Nb3Sn strands. The cable-in-channel of reacted Nb3Sn strands are then wound to fabricate a superconducting coil. The Nb3Sn superconducting coil can be used, for example, in a magnet structure for particle acceleration. In one example, the superconducting coil is used in a high-field superconducting synchrocyclotron.