Double-Helix Coil Technology for Bent Accelerator Magnets

High field superconducting dipole magnets, with a field strength of about 4.5 Tesla and a bend radius of about 0.7 m, are required in the high radiation areas of beam transport in future rare isotope accelerators. However, the small bending radii of these magnets produce unwanted higher-order harmonics in the magnetic field, which are detrimental to accelerator operation. This project will develop a novel coil design, the double-helix dipole, which provides an inherent ability to cancel unwanted higher order harmonics. The double-helix dipole employs helical windings on composite or moldable ceramic coil forms, thereby creating very robust coil structures, as needed for reliable superconducting magnets. Phase I designed a bent dipole magnet to meet the specifications of the planned Rare Isotope Accelerator (RIA). It was shown that the higher-order harmonics caused by the bending radius of the coil could be compensated by modifying the conductor path of the double-helix coils, thus allowing the magnet to meet field quality requirements. A manufacturing process for double-helix coils was developed, and two prototype coil windings were manufactured and shock tested with liquid nitrogen to qualify the constituent materials for cryogenic applications. During Phase II, two superconducting magnets will be manufactured and cryogenically tested at a national laboratory. The first magnet will be a short straight coil without iron yoke to qualify the superconducting cable and the manufacturing technology. The second magnet will be a prototype bent magnet with iron yoke. Field measurements will be performed at operational temperature, in order to verify the method of compensating for higher-order multipole components in the winding itself. Commercial Applications and Other Benefits as described by the awardee: The bent double-helix magnets should be an important contribution to accelerator magnet design for planned rare isotope accelerators. In addition, the high uniform field and the low manufacturing cost would make the technology an ideal fit for use in the field of proton therapy. The coil technology also should be suitable for use in rotors and stators of high power electrical machinery.