The National High Magnetic Field Laboratory (NHMFL) has successfully operated its 20 Tesla 195 mm large bore magnet for over 20 years. Eventually, as there was a certain slowdown in demand for that magnet at the time, it had been decommissioned in 2016 and its two outer coils have been re-used for parts in a higher energy density configuration to facilitate the fast construction of the world record 41.5 Tesla 32 mm bore resistive magnet. Without any resistive large bore magnet providing fields in the 20 Telsa range available for the last two years, the demand or desire for such a facility has been steadily rising at our laboratory. Again, cost and schedule for the construction of such a magnet are very critical aspects under consideration. One elegant solution to keep these factors most manageable is to not design a new stand-alonemagnet but to design one or a set of insert coils that is interchangeable with a smaller bore existing magnet at the NHMFL. Different alternative configurations for such a large bore resistive insert including two different existing magnets to serve as the outsert as well as different usable bore sizes have been considered on a preliminary level of detail for comparison only. Eventually, a more detailed conceptual design has been developed for a chosen magnet system. In this paper, the authors present a summary of the different alternative considerations as well as an introduction to the conceptual design of a next generation 195 mm Large Bore Magnet capable to produce well above 20 Tesla.

The National High Magnetic Field Laboratory has commissioned a 36.1 T resistive/superconducting hybrid magnet with homogeneity and stability of 1 ppm over a 10 mm diameter spherical volume to be used for solid-state nuclear magnetic resonance (NMR). Most NMR magnets use single strands of superconducting wire carrying a few hundred amps and persistent joints and switches. This magnet uses a 20 kA superconducting cable in a steel conduit for the outer part of the magnet and copper-alloy sheet metal for the inner part of the magnet. While >15 hybrid magnets have been built worldwide, they typically have a field uniformity of ~250 ppm/cm DSV and stability might be no better than 50 ppm. To attain 1 ppm uniformity, current density grading was employed in the resistive coils to cancel the z2 term. In addition, coils were shifted after the first map to reduce the z1 term. Ferroshims and resistive shims were installed in the bore to attain <;1 ppm over 10 mm. The large inductance of the superconducting coil reduced the ripple sixfold compared with all-resistive magnets and essentially eliminated the 60 Hz ripple and its harmonics. An NMR lock reduced the low-frequency drift to attain ~0.1 ppm stability.

The National High Magnetic Field Laboratory (NHMFL) has developed the design of its next generation 32-mm bore resistive magnet. This magnet upgrade includes enlarging the size of the outmost coil from a 610 mm to a 1000 mm outer diameter and from a 430 mm to a 731 mm maximum height. First, a general design optimization was performed to decide on the number, the geometries and the materials of the nested resistive coils. As a result of that analysis, a six coil design was chosen (upgraded from four coils) with the innermost two coils electrically connected in parallel and the remaining coils connected in series. Next, a series of systematic detailed analyses of the winding pack were iterated coil by coil as well as section by section along each coil axis employing current density grading all in an effort to achieve a new world record field of 41.5 Tesla. The project was executed within an aggressive 2.5 years total time line from the start of the earnest design to completion of the fabrication drawing package taking the first year followed by a 1.5 year period for procurement and construction. Finally, first testing of this water-cooled magnet has just been concluded in August 2017, including the collection of hydraulic pump curves and a first successful charge to the full current of 48 kA. An extrapolated hall-probe measurement suggests this 32-mm bore all-resistive magnet generated a 41.4 T(+/- 0.2 T) peak field consuming 31.9 MW of electrical power leaving a 5% voltage margin towards the available 700 V limit. Minimal further winding adjustments accompanied by accurate field calibrations are planned next to tune and confirm the magnet to 41.5 T before it is delivered to the NHMFL user program in the near future.

The system integration of a 36 T high field resistive-superconducting hybrid magnet system which will be used primarily for NMR studies is being finalized at the National High Magnetic Field Laboratory in Tallahassee, Florida. The hybrid magnet consists of a 23 T resistive insert coil set nested inside of a 13 T superconducting coil wound with high JC Nb3Sn/Cu cable-in-conduit conductor. The resistive and superconducting coils are connected electrically in series and operate at 20 kA. The combined system will enable 1-ppm level uniformity in a 1 cm DSV for condensed-matter NMR at a record level of 1.53 GHz. The resistive insert has four concentric Florida-Bitter coils and operates at 14 MW. The superconducting outsert operates with forced flow supercritical helium at 4.5 K and 3.5 bar. The superconducting protection system consists of two fully independent circuits, one employing voltage averaging comparisons between winding layers and the other a voltage comparison with a co-wound coil. Initial magnet testing of the resistive coils has been completed. The superconducting cold mass has been cooled to 4.5 K and the system is being prepared for combined hybrid magnet testing.

The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48mm magnet bore and 42mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used. Field maps corrected for field instabilities were obtained and shimming achieved better than 1ppm homogeneity over a cylindrical volume of 1cm diameter and height. The magnetic field is regulated within 0.2ppm using an external 7Li lock sample doped with paramagnetic MnCl2. The improved field homogeneity and field regulation using a modified AVANCE NEO console enables NMR spectroscopy at 1H frequencies of 1.0, 1.2 and 1.5GHz. NMR at 1.5GHz reflects a 50% increase in field strength above the highest superconducting magnets currently available. Three NMR probes have been constructed each equipped with an external lock rf coil for field regulation. Initial NMR results obtained from the SCH magnet using these probes illustrate the very exciting potential of ultra-high magnetic fields.

The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1 T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48 mm magnet bore and 42 mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used. Field maps corrected for field instabilities were obtained and shimming achieved better than 1 ppm homogeneity over a cylindrical volume of 1 cm diameter and height. The magnetic field is regulated within 0.2 ppm using an external Li-7 lock sample doped with paramagnetic MnCl2. The improved field homogeneity and field regulation using a modified AVANCE NEO console enables NMR spectroscopy at H-1 frequencies of 1.0, 1.2 and 1.5 GHz. NMR at 1.5 GHz reflects a 50% increase in field strength above the highest superconducting magnets currently available. Three NMR probes have been constructed each equipped with an external lock rf coil for field regulation. Initial NMR results obtained from the SCH magnet using these probes illustrate the very exciting potential of ultra-high magnetic fields. (c) 2017 Elsevier Inc. All rights reserved.

The National High Magnetic Field Laboratory has designed and built cryostats for two series-connected hybrid (SCH) magnets. The first one is for the Helmholtz Center Berlin. Its cryostat is designed to support up to 8 MW of resistive insert inside a water-cooled housing that has a conical warm bore with a 30-degree opening angle and a 5-ton superconducting outsert coil that is housed in a vacuum vessel. Normal operation includes 28 bar of water pressure and 52 kN of side load between the resistive insert coils and the superconducting outsert coils due to a potential 3-mm coil misalignment. Under a fault condition, the resistive coils can generate axial loads of up to 1.1 MN. The second cryostat for the Florida State University SCH houses the same superconducting outsert, but its resistive insert is a high-homogeneity solenoid. The system is designed to support a high-field 14-MW insert, operated at 30-bar water pressure, up to 42-kN side load, and 2.6-MN fault forces. Numerous complex two-dimensional and three-dimensional finite-element models have been developed and used for a systematic optimization of all critical load path items.

The National High Magnetic Field Laboratory (NHMFL) has developed series-connected hybrids (SCHs) each comprising of a superconducting outsert built with Nb3Sn cable-in-conduit conductor and a resistive insert using Florida Bitter technology. The first SCH, to be operated at the Helmholtz Center Berlin, has been tested successfully generating a central field above 25 T in a horizontal conical warm bore with a 30° opening angle suitable for neutron scattering experiments. The resistive insert contributing 13 T includes two coils electrically in series with a total power consumption of 4.4 MW. The second SCH, to be installed and operated at the NHMFL, has a target to provide 1-ppm maximum field inhomogeneity in a 36-T 40-mm bore for medium-resolution nuclear magnetic resonance science. The resistive insert contributes 23 T and includes four coils electrically in series with a total power consumption of 14 MW. The innermost two resistive coils include axial current grading targeting unshimmed field uniformity below 100 ppm over a 10-mm-diameter spherical volume. The design of the resistive insert for the second SCH was completed in mid-2014, and this project is currently in the final construction phase.

Helmholtz-Zentrum Berlin (HZB) operates two large-scale facilities: the research reactor BER 2 and the synchrotron source for soft X-rays BESSY 2. This year HZB's neutron instrument suite around BER 2 has been strengthened by a unique high-magnetic-field facility for neutron scattering. Its main components are the High Field Magnet (HFM), which is the most powerful dc magnet for neutron scattering worldwide, and the Extreme Environment Diffractometer (EXED), which is a dedicated neutron instrument for time-of-flight technique. The hybrid magnet system is projected according to the special geometric constraints of analyzing samples by neutron scattering in a high field magnet. Following our past experience, only steady-state fields are adequate to achieve the goals of the project. In particular, inelastic scattering studies would virtually be excluded when using pulsed magnets. The new series-connected hybrid magnet with a horizontal field orientation was designed and constructed in collaboration with the National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL, USA. With a set consisting of a superconducting cable-in-conduit coil and different resistive coils of conical shape, maximum fields between 26-31 T are possible with cooling power between 4 and 8 MW for the resistive part. A series of commissioning activities of the magnet components and the technical infrastructure systems (20-kA power supply, water cooling, and 4-K Helium refrigerator) was completed at HZB. The maximum field achieved with a 4-MW resistive coil was 26 T.

The National High Magnetic Field Laboratory has developed and operated large, high-field dc and pulsed magnets for research in condensed matter physics. We are now developing three resistive/superconducting hybrid magnets with fields ranging from 25 to 45 T, and are developing concepts for hybrid magnets up to 60 T as well human-head MRI magnets up to 20 T and repetitively pulsed magnets to reach 60 T every 30 sec.

The final assembly of the Series-Connected Hybrid magnet system for the Helmholtz-Zentrum Berlin for Materials and Energy (HZB) has occurred with the integration of the superconducting cold mass, cryostat, resistive Florida-Bitter coils, and the cryogenic, chilled water, power, and control subsystems. The hybrid magnet consists of a 13-T superconducting Nb3Sn/CICC coil and a set of 12-T resistive, water cooled coils at 4.4 MW. Much of the cryostat and cold mass functional requirements were dictated by the electromagnetic interactions between the superconducting and resistive coils. This includes the radial decentering and axial aligning forces from normal operations and a 1.1 MN fault load. The system assembly was an international achievement with the cold mass being completed at the NHMFL in the USA, cryostat to cold mass interfaces made at Criotec Impianti in Italy, and final assembly at the HZB in Germany.

The first Series Connected Hybrid (SCH) Magnet presently being designed and built at the NHMFL has targeted 36 T with 1 ppm maximum inhomogeneity over a 10-mm-diameter spherical volume at the midplane of a 40-mm clear bore for scientific users interested in medium resolution NMR studies. The SCH comprises a 13 T superconducting outsert built with Nb3Sn cable-in-conduit conductors, a 23 T resistive insert using Florida-Bitter technology, and water-cooled resistive shims providing up to 90 ppm correction. The insert and outsert are connected electrically in series. Inhomogeneity predictions for the unshimmed SCH were made using various finite element analyses on a preliminary SCH design. Manufacturing tolerances were benchmarked by performing a sensitivity analysis and comparing the finite element analyses results to inhomogeneity measurements on the Keck and Cell 2 magnets, two NHMFL magnets, which represent the state-of-the-art for producing high homogeneity fields with resistive Florida-Bitter technology. Next, the shim terms from the measured and predicted 3-D field maps were analyzed with an NHMFL in-house code, which provided the inhomogeneity specification of the unshimmed SCH. Finally, a design of the SCH water-cooled resistive shims was developed based on all the measured and calculated data including additional engineering safety factors. This analysis is an essential step for achieving the targeted overall performance of a record 1 ppm inhomogeneity at 36 T.

The NHMFL has developed a high-field split resistive magnet for use in far-infrared photon scattering experiments. The magnet includes four large scattering ports of elliptical shape at the mid-plane amounting to a total solid angle of 0.5 steradians of available user space. Such a magnet configuration results in unique design challenges being especially severe for the windings in the mid-plane region of the innermost coils. Consequently, the NHMFL developed, tested and employed a new technology called Split Florida-Helix. Next, the coil design of the split user magnet, to be operated at our own facility, has been completed in 2009. This user magnet consist of 5 resistive coils consuming a total of less than 28 MW of dc power and providing a flux-density of 25 T available to the user space. To meet the unique design challenges, Split Florida-Helix technology is used around the mid-plane of the two inner most coils and state-of-the-art Florida-Bitter technology is used for all the regular winding in all 5 coils.

The NHMFL has completed the design of all major components of a high-field split resistive magnet for use in far-infrared photon scattering experiments. The magnet includes four large scattering ports of elliptical shape at the mid-plane. Such a magnet configuration results in unique design challenges being especially severe for the windings in the mid-plane region of the innermost coils. Consequently, the NHMFL incorporated its newly developed technology called split Florida-Helix previously tested at the NHMFL with diverse working models. The user magnet, to be operated at our own facility, will consist of 5 resistive coils consuming a total of less than 28 MW of dc power and providing a flux-density of at least 25 T available at the center of the user space. All coils employ axial current grading for field optimization and stress management. Advanced finite element analysis (FEA) served as the essential tool guiding the design optimization of the overall system and the various components. This paper provides a systematic discussion of the critical features and techniques utilized in the complex model-based analysis and the authors present a variety of detailed FEA results and design parameters critical for the integration of the split Florida-helix in conjunction with the traditional Florida Bitter disc design.

The National High Magnetic Field Laboratory (NHMFL) is designing two series-connected hybrid magnets, one for the Helmholtz Center Berlin (HZB) and the other for the NHMFL. The one for HZB has a horizontal, conical warm bore with a 30 degree opening angle for neutron scattering experiments. The one for the NHMFL has a 40 mm diameter vertical warm bore with a cylindrical profile. The design of the HZB cryostat will be completed this year. In this paper the design of the HZB cryostat is presented. The results of a structural analysis performed for normal operation and for fault scenario are discussed. The main features of the NHMFL cryostat are described shortly in the introduction section.

The National High Magnetic Field Laboratory is developing resistive-superconducting hybrid magnets both for internal use and for installation at other facilities. The Tallahassee magnet will have a vertical bore and provide 36 T in a 40-mm bore with 1-ppm homogeneity over a 10-mm diameter spherical volume. The Berlin version will provide a horizontal field of 25 T in a converging-diverging bore configuration suitable for neutron-scattering experiments. A design study is underway for a third magnet for Oak Ridge that will be similar to the Berlin version but provide >30 T. The three magnets will use very similar ~ 13 T Nb3Sn CICC coils for the superconducting outserts. The resistive insert magnets will be different configurations operating at different power levels. In designing the magnet systems we have developed a new numerical model to predict the critical current of Nb3Sn CICC's, tested several conductors in-house and abroad, designed cryostats and refrigeration systems, and developed new resistive magnet technology. An overview of the innovations and present status is presented.

The NHMFL is developing a high-field split resistive magnet for use in far-infrared photon scattering experiments. The magnet will include four large scattering ports of elliptical shape at the midplane. Such a magnet configuration results in unique design challenges being especially severe for the windings in the midplane region of the innermost coils. Consequently, the NHMFL developed a new technology called split Florida-helix. To test and demonstrate those new concepts, the NHMFL recently completed the design and fabrication of a working model of a split Florida- helix. Advanced 3-D finite element analysis (FEA) served as the essential tool guiding the design optimization. This paper provides a systematic discussion of the critical features and techniques utilized in the complex model-based analysis including orthotropic material properties, actual non-symmetric current and load distributions as well as turn-to-turn frictional contact and sliding. Furthermore, the authors present a variety of detailed FEA results that prove to be fundamental for a successful application and integration of the split Florida-helix. Critical design decisions are discussed.

We present details of the specifications and performance of the new 50 mm bore, 30 T resistive magnet that has been commissioned at the Nijmegen High Field Magnet Laboratory in May 2007. The two innermost Florida-type Bitter coils will also be used in the 30 T, 10 MW hybrid magnet to be completed in 2008.

The National High Magnetic Field Laboratory is developing several powered magnets employing novel configurations for use in photon and neutron scattering experiments. First is a split resistive magnet being built for Far-Infrared Scattering at the NHMFL in Tallahassee. This magnet has spurred the development of the novel Split Florida-Helix (SFH) technology. High-field test coils of the SFH concept have been designed and built. Test results are presented. Second, Series-Connected Hybrid magnets with horizontal, conical bores are being designed for neutron scattering experiments at the Hahn-Meitner Institute in Berlin and the Spallation Neutron Source in Oak Ridge, TN. A new resistive magnet technology, the Conical Florida-Bitter (CFB), is being developed suitable for use as the resistive insert of these magnets. A high-field CFB test coil has been designed and is under construction. The conceptual design of the eventual hybrid system is presented along with the detailed design of the high-field test coil.