H.J. Schneider-Muntau

High Field Superconducting Solenoids Via High Temperature Superconductors

High-field superconducting solenoids have proven themselves to be of great value to scientific research in a number of fields, including chemistry, physics and biology. Present-day magnets take advantage of the high-field properties of Nb3Sn, but the high-field limits of this conductor are nearly reached and so a new conductor and magnet technology is necessary for superconducting magnets beyond 25 T. Twenty years after the initial discovery of superconductivity at high temperatures in complex oxides, a number of high temperature superconductor (HTS) based conductors are available in sufficient lengths to develop high-field superconducting magnets. In this paper, present day HTS conductor and magnet technologies are discussed. HTS conductors have demonstrated the ability to carry very large critical current densities at magnetic fields of 45 T, and two insert coil demonstrations have surpassed the 25 T barrier. There are, however, many challenges to the implementation of HTS conductors in high-field magnets, including coil manufacturing, electromechanical behavior and quench protection. These issues are discussed and a view to the future is provided.

An overview of the 45-T hybrid magnet system for the new National High Magnetic Field Laboratory

The new National High Magnetic Field Laboratory (NHMFL) at Tallahassee, Florida is committed to putting into operation in 1995 a 45-T Hybrid Magnet System to support research in steady, high magnetic fields. This facility will be accessible by qualified users world-wide on the basis of proposal and review. The more prominent components of this system will be a 24-MW resistive insert and a 120-MJ superconducting outsert. But successful achievement of the performance goals for the 45-T Hybrid System will depend on a number of unique, state-of-the-art subsystems and components. This paper describes the requirements and specifications on the individual subsystems and components in the context of the overall performance gears and reviews the plan for putting the whole together. >

A new concept in Bitter disk design

A new concept in cooling hole design in Bitter disks that allows for much higher power densities and results in considerably lower hoop stresses has been developed and successfully tested at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, FL. The new cooling hole shape allows for extreme power densities (up to 12 W/mm/sup 3/) at a moderate heat flux of only 5 W/mm/sup 2/. The new concept also reduces the hoop stress by about 30-50% by making a Bitter disk compliant in the radial direction through staggering small width and closely spaced elongated cooling holes. Finally, the design is optimized for equal temperature.

Design of a poly-Bitter magnet at the NHMFL

The worlds first 33 Tesla resistive magnet is being designed and built at the National High Magnetic Field Laboratory in Tallahassee, FL. Completion of the magnet is expected in the fourth quarter of 1995. It will produce a peak on-axis field greater than 33 Teslas in a 32 mm warm bore while consuming 20 megawatts of power. This magnet consists of two small concentric parallel coils (poly-Bitter) in series with two larger Bitter coils. Details of optimization calculations and the resulting magnet design and construction are presented.

The world's first 27 T and 30 T resistive magnets

We describe in detail a 30 Tesla, 32 mm warm bore, 15 MW resistive magnet which was put into operation at the National High Magnetic Field Laboratory in Tallahassee, FL in March 1995. The magnet consists of three concentric axially-cooled Bitter stacks connected electrically in series. This magnet employs a substantial new development in Bitter magnet technology which allows high current densities without the usually accompanying high stresses. Details of magnet optimization, design, construction, testing and operation are presented. We also report on operating experience with the 27 T magnets.

High performance pulsed magnets with high strength conductors and high modulus internal reinforcement

The use of internal reinforcement in pulse magnets has been proven to be an efficient way to obtain reliably very high magnetic fields. An optimum design should be such that both the reinforcement and the conductor reach their failure criteria simultaneously. This requires the mechanical properties of the reinforcement to match those of the conductor under all operating conditions. The decision criterions for the selection of the internal reinforcement materials for different conductors are presented and discussed. Several pulsed magnets with high strength conductors and internal reinforcement with high modulus materials have been designed, fabricated and tested. The performance of these magnets is presented and discussed.

The 45 T hybrid insert: recent achievements

The NHMFL hybrid magnet was successfully tested to 45.1 T in an air bore as designed on June 26, 2000. The magnet consists of a cable-in-conduit superconducting outsert producing 14.3 T in a 616 mm bore and a Florida-Bitter resistive insert providing 30.8 T in a 32 mm bore. The insert was tested without the outsert in May 1999. The combined system was tested in December 1999 reaching a peak field of 44 T in an air bore. Physics experiments were run in December 1999 at 45 T using dysprosium pole piece flux concentrators. During the first and second quarters of 2000 modifications were made to the cryogenic system and the resistive insert. Test results of the resistive insert from December 1999 to June 2000 are presented along with a discussion of the possibilities of upgrading the insert to reach a total field of 50 T. Scientific experiments are scheduled up to 45 T in a clear bore starting July 3, 2000. A spare set of resistive coils is under construction.

Test results and potential for upgrade of the 45 T hybrid insert

Construction of the NHMFL hybrid magnet is complete. The resistive insert was tested to full current without the background field from the superconducting magnet on May 17, 1999. Tests of the combined system have been scheduled for October 1999. The resistive insert fits into the 616 mm bore of the 14 T outsert superconducting magnet. The insert consists of a five coil, axially cooled Florida-Bitter design. The two innermost coils are electrically in parallel and this pair is in series with the other four coils. The magnet design uses Florida-Bitter disks made of Cu-Ag, Cu-Be, Cu-Zr and Cu sheet and is heavily based upon the high field resistive magnets previously built at the NHMFL. Details of the coil design, construction and testing are presented.

25 T high resolution NMR magnet program and technology

The program at the National High Magnetic Field Laboratory for the design and development of 1 GHz class NMR magnets is described. The parameters are given for a 1.066 GHz magnet incorporating an HTS inner coil. The design of the related wide bore 900 MHz conventional superconductor magnet is described. Aspects of the technology development program supporting these designs are presented.

The US 100 T magnet project

Abstract A design is presented of a 100 T research magnet to generate high field pulses having lengths of more than 20 ms at field levels of above 80 T. The magnet is designed to be nondestructive, have a bore of 24 mm and a repetition rate of less than 1 h. It consists of a 50 T outer magnet, constructed of five concentric, mechanically independent coils, powered from a motor-generator, and a self-supporting 50 T insert magnet, which is energized from a capacitor bank. The design is based on commercially available materials. The magnet has an overall diameter and total length of approximately 1 m.