Conduction cooled superconducting magnet for low cost, compact proton therapy systems

Solid Material Solutions, Llc, North Chelmsford MA

Investigators

Abstract

Superconducting magnets are required that enable large-bore, higher field magnets to be reduced in size, weight, cost and with improved cooling in medical equipment and systems applications. High Temperature Superconductors (HTS) provide the best options for advancing these systems to higher fields and operating temperatures that are attained with Liquid Helium ? free refrigeration, provided they can be made with the required form, strength, uniformity and current density (Je) into high current, flexible cables, and those cables wound into sufficiently small diameter, high field coils. Among HTS options, only the ?1G? Bi2223 (Bi2Sr2Ca2Cu3Ox) oxide in silver (Ag), and with added reinforcement, can presently meet all the requirements for these kinds of large scale commercial magnet applications. Most recently, an extra strong and flexible 1G tape called Type NX, that is reinforced with a superalloy, has been developed and commercialized. Its availability now enables development and demonstration in this program of the feasibility of large bore (~1 m dia.), high field (8T to10T) coils, wound with an NX based cable that can be conduction cooled and operated at 20K, rather than liquid cryogen cooled to 4K, as is required with presently available Low Temperature Superconductors (LTS). In this Phase 1 SBIR program, we will establish and prove the technology for producing long lengths of flexible 2 kA(8T, 20K) cable with Type NX, and from these cables, producing 0.8 m inner diameter test and demonstration solenoid coils with key features for building on order 1 m diameter, high field magnet coils. As a first step, we will develop a cable design with 8 high strength Type NX 1G tapes as a baseline, along with length production capability. The tooling and wire handling, as well as machine settings and procedures for producing long cables will then be established, and cables produced for coil development. In the next step, relatively short lengths of cable will at first be used to establish coil winding procedures, and then produce coils with pancake and level wind configurations, all with a 0.8 m diameter base. These coils will be tested for both cable and constituent wire Ic?s in different cooling environments, as well as dimensions and cooling and heat transfer characteristics. As a final step, several coils will be produced with longer lengths of cable, and their properties tested, culminating in a coil with about half the radial build required to achieve 8 T at 20 K with 0.8 m diameter, and proving that a conduction cooled magnet suitable for commercial medical equipment applications is feasible by the combination of our cable and coiling techniques. When fully developed in a Phase 2 program, this advance will enable the practical production of much higher field, large bore magnets that can be operated in a conduction cooled mode, for example at 20K, and that are overall, quite compact and inexpensive to operate, with application in medical instruments and devices.