R.J. Weggel

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. >

Hybrid III: The system, test results, the next step

The authors describe the overall Hybrid III system, present test results, and indicate future plans. Hybrid III, completed in late 1991, has since undergone a sequence of tests in preparation for becoming a facility magnet. When first tested in December 1991, it generated a total central field of 33.5 T. The superconducting magnet (SCM), operating in a bath of superfluid helium at 1.65 K and with a current of 2200 A, contributed 12.7 T to the total. In subsequent runs it was shown that the SCM would reach a critical current of approximately 2230 A when operated at approximately 1.7 K. After the completion of improvements to the cryogenic components as described, two major goals were set: to reach 35 T in two steps and to operate Hybrid III as a facility magnet. Hybrid III is targeted to reach 35 T in the spring of 1993.<<ETX>>

Hybrid III system

A magnet system known as Hybrid III under construction at the Francis Bitter National Magnet Laboratory, is described. The superconducting magnet will consist of a Nb/sub 3/Sn magnet surrounded by a NbTi magnet. In a departure from earlier design philosophy, the NbTi magnet is not designed to be cryostable; it is provided with only enough cooling to cope with nominal dissipations generated by joints and field sweeps. The magnet is therefore referred to as a quasi-adiabatic magnet. The aim of the quasi-adiabatic concept is to make a magnet sufficiently adiabatic that there will not be hot spots in the event of a quench, and yet cooled well enough to ride out steady dissipations. The cryostat can operate at 1.8 K and at 4.2 K. The superconducting section is designed to generate 13 T at 1.8 K. The system is to reach 35 T, or perhaps more as water-cooled inserts are developed. >

A design for the superconducting outsert of a 45-T hybrid magnet system using cable-in-conduit conductors

A part of the mission of the new NHMFL is to have available for users in 1995 a hybrid magnet system capable of producing at least 45-T steady field on axis in a 33-mm working bore. Approximately 31 T of the combined field will be produced by a water-cooled insert. The superconducting outsert, which combines NbTi and Nb/sub 3/Sn conductor technologies, will provide more than 14 T. The authors describe an option for this superconducting outsert based on the cable-in-conduit-conductor (CICC) approach, where cabled strands of conductor are contained in intimate contact with helium coolant inside a strong steel sheath that also acts as distributed structure. A departure from the usual practice for CICC technology is in the application of static Hell cooling, which simultaneously provides higher conductor performance and nearly passive extraction of the rather modest heat loads during normal operation of the magnet system.<<ETX>>

The monohelix: (1) five years of operation at the FBNML and (2) finite element stress analyses

The FBNML (Francis Bitter National Magnet Laboratory) has built and operated seven partial monohelices employing helices of Be-Cu, Cu-alumina, or Cr-Cu. Fabrication was by conventional lathe, numerically controlled lathe, or wire electric discharge machining. Each monohelix is the innermost coil of a hybrid magnet system which can generate 27 T in a 53-mm bore or 31 T in a 33-mm bore (35 T with holmium poles). Compared to their Bitter coil predecessors, these monohelices have demonstrated comparable performance and superior life. One helix gave 270 hours of service; another is still active after 230 hours. The finite element stress analysis program ABAQUS was used to calculate the stresses and strains in radially cooled Bitter coils and monohelices. At a maximum conductor strain of 0.8% (the approximate empirical limit for acceptable coil life), a perfect monohelix is structurally a third stronger than the Bitter coil analyzed. The strength of the partial monohelix design appears to depend on the relative thicknesses of the helix and cooling plates, and on the friction between them. >

The development of a niobium-titanium cable-in-conduit coil for a 45 T hybrid magnet

A 35 T Hybrid magnet is to be installed at the National High Magnetic Field Laboratory at Tallahassee. The superconducting background field magnet of this system consists of three coils, two of niobium-tin conductor and one of niobium-titanium. This paper describes the design and construction of the niobium-titanium section. In the design, three issues of principal importance were considered: stability and dissipation under pulsed and steady state conditions; the stressing of the conduit, and the consequences of quenching. The details of construction have centered around the winding and assembly of the pancake coils and the preparation of the joints. The construction of the coil is part of a collaborative program between MIT and FSU. >

Monohelix research at the MIT Magnet Lab

A discussion is presented of the radially-cooled monohelix to support the high stress and power densities within the highest-field magnets at Francis Bitter National Magnet Laboratory. The design employs a continuous machined helical conductor (to eliminate the radial slits which weaken the Bitter design) whose helical winding is built up from annular plates. The first monohelix is the inner of two coils which constitute the water-cooled insert of a hybrid system of 53-mm bore. The system generates 27.1 T. The coil experiences average hoop stresses up to 370 MPa, and heat fluxes up to 7.2 W/mm/sup 2/ in passages only 0.25-mm deep. >

Hybrid magnet program at the Francis Bitter National Magnet Laboratory MIT

The authors chronicle the evolution of hybrid magnets built at the Francis Bitter National Magnet Laboratory. It is noted that resistive water-cooled magnets can generate field according to how much power is available. The hybrid concept has been developed for generating fields beyond a power limit, up to 45 T. Along the way five successively more adventurous designs have been tried. >

35 Tesla hybrid magnet

Abstract A superconducting magnet, consisting of concentric Nb 3 Sn and NbTi coils, will operate in a bath of subcooled helium at 1.8 K in a quasi-adiabatically stable mode. Water-cooled 10 MW insert magnets which fit within the 36 cm cryostat bore are based upon a design which has proven very successful. The system will provide researches with ultrahigh continuous magnetic fields.

A 17-tesla magnet with multiple radial access ports

A description is given of the design and construction of a magnet generating over 17 T with multiple radial access ports to allow water cooling. There are seven ports, 19-mm high, at 30 degrees intervals around half the circumference of the magnet midplane. The magnet consists of a split pair of coils of 330 mm (outer diameter) and 100-mm length spaced 23 mm apart. Together they consume approximately 8.5 MW. They are Bitter coils with cooling provided by water flowing outward through shallow passages etched in the plates. Heat fluxes are as high as 700 W/cm/sup 2/. In an unusual overall configuration, hydraulics, coil clamping, support, and electrical connections were all made as unobtrusive as possible. >