Concentric Tilted Double-Helix Dipole Magnets

70211 The high magnetic fields required for future accelerator magnets can only be achieved with Nb3Sn or other A15 or HTS type conductors, which are brittle and sensitive to mechanical strain. The traditional ¿cosine-theta¿ dipole configuration for these magnet designs has intrinsic drawbacks that make it difficult and expensive to employ such conductors. These drawbacks include: (1) difficulty in applying enough pre-stress to counteract Lorentz forces without compromising conductor performance; (2) the small minimum bend radii of the conductor, necessitating the intricate wind-and-react coil fabrication; (3) complex spacers for coil ends and expensive tooling for coil fabrication; and (4) the limited fraction of the coil aperture that can be used with achievable field uniformity (typically only 2/3 can be used). This project will develop a coil configuration that produces dipole fields based on tilted solenoidal windings. Using concentric pairs of helical coils with opposite tilt, the solenoid fields are exactly canceled and the dipole field components add. The coil configuration will have significantly smaller systematic errors without the use of any field forming spacers and will be simpler and less expensive to manufacture than traditional cosine-theta coils. In Phase I, a 1-meter long, double-helix coil with a ~2-tesla dipole field will be designed and fabricated using NbTi superconducting cable. This model magnet will be cryogenically tested at a national laboratory. The application of pre-reacted Nb3Sn conductor and HTS tapes for the proposed design will be studied. Commercial Applications and Other Benefits as described by the awardee: The double-helix dipole offers significant cost and performance advantages for accelerator magnets. The simple solenoidal coil geometry should lower the cost of many applications where dipole fields are needed such as magneto-hydrodynamic thrusting devices and for rotors and stators in superconducting electrical machinery.