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.

REBCO high-temperature superconductors (HTS) are being utilized to extend the limits of dc solenoidal magnetic fields to 32 Tin a user magnet. It is reasonable to expect that these field limits will continue to be surpassed resulting in higher stored energy coils. These larger coils will require kilo-amp level currents to reduce their inductance to manageable levels. Lower inductance coils will be necessary to eliminate unacceptably long ramp times and expensive high voltage isolation hardware by reducing inductive charging and quench voltages. A novel high-current coil concept, using an integrated coil form (ICF), is described here. The coil concept is being developed in combination with a high-current flux pump at the University of Cambridge. The first test coil will be charged to 5.6 kA and will demonstrate the ICF coil winding technique, current lead connections, layer transitions, and coil terminations, as well as ramping and quench performance. The test coil design is described.

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 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.

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 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 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 National High Magnetic Field Laboratory (NHMFL) is designing series-connected hybrid magnets for the Helmholtz Center Berlin (HZB). The hybrid has a horizontal, conical warm bore with a 30 degree opening angle for neutron scattering experiments. The resistive insert includes two coils. The outer coil is a regular bitter coil, while the inner one has a varied inner radius to meet the requirement of large opening angle. Such technology as in the inner coil was developed in the NHMFL, and called Florida conical bitter technology. The conical configuration makes the cooling hole length varied with radius causing unique hydraulic design challenge. This paper presents the detail design features of the conical insert along with many analysis results.

The NHMFL Series Connected Hybrid (SCH) magnet will provide an energy-efficient 36 T to the DC user facility by employing a 20 kA superconducting outsert coil in series with a resistive insert. The magnet outsert consists of three concentric layer-wound sub-coils using three different grades of Nb 3 Sn Cable-in-Conduit Conductors (CICC). The electrical joints in the superconducting outsert require low DC resistance to minimize the refrigeration requirement at the operational 4.5 K temperatures and low AC losses to ensure good stability against ramping operation required by the users. There are four internal splice joints in the outsert, which are Nb 3 Sn to Nb 3 Sn joints with the same design configuration. There are another two terminal joints between the Nb 3 Sn outsert and the two NbTi buslines, which connect the outsert terminals to the two current leads. The two Nb 3 Sn to NbTi terminal joints are of identical configurations. All of the joints will be praying-hands configuration with an operation current of 20 kA. The R&D for the joins has been carried out at the NHMFL. The joints design and test results are discussed in this article.

The National High Magnetic Field Laboratory (NHMFL) has designed and is constructing a Series-Connected Hybrid (SCH) magnet system in Tallahassee, FL. Before the construction of the magnet system can begin many obstacles have to be solved through hardware design and winding practices. The hardware has to have the strength to handle the stresses of winding as well as retaining maximum functionality. The NHMFL will overcome these issues by running several analysis calculations and by producing three model coils for practicing functionality. Two model coils have been built and necessary changes to design and winding procedures have occurred through the practices. These changes will be presented and have been implemented into our winding procedures.

The National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida has designed and is now constructing two Series Connected Hybrid (SCH) magnets, each connecting a superconducting outsert coil and a resistive Florida Bitter insert coil electrically in series. The SCH to be installed at the NHMFL will produce 36 T and provide 1 ppm maximum field inhomogeneity over a 1 cm diameter spherical volume. The SCH to be installed at the Helmholtz Center Berlin (HZB) in combination with a neutron source will produce 25 T to 30 T depending on the resistive insert. The two magnets have a common design for their cable-in-conduit conductor (CICC) and superconducting outsert coils. The CICC outsert coil winding packs have an inner diameter of 0.6 m and contribute 13.1 T to the central field using three grades of CICC conductors. Each conductor grade carries 20 kA and employs the same type of Nb3Sn superconducting wire, but each grade contains different quantities of superconducting wires, different cabling patterns and different aspect ratios. The cryostats and resistive insert coils for the two magnets are different. This paper discusses the progress in CIC conductor and coil fabrication over the last year including specification, qualification and production activities for wire, cable, conductor and coil processing.

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) has several resistive solenoid magnet projects underway presently, including upgrade of four existing magnets, design of the conical bore insert for the Helmholtz Center Berlin (HZB), design of insert coils of the Series-Connected-Hybrid (SCH) for NHMFL and design of resistive split magnet. The upgrades and the design of the conical bore insert are discussed in detail while other programs are presented briefly.

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.

Here, we report the development of the CICC joint design for the 36-T Series-Connected Hybrid Magnet. A novel solder-less single-box praying-hands joint has been designed to meet the mission of the SCH. A prototype sample joint, Florida Solder-less Joint A (FSJ-A), was manufactured and tested. The low DC resistance confirmed the feasibility of the concept design. In addition, a simple model describing the current transient behavior of the pray-hand joint is presented. A comparison with the experimental data is also included.

The development of the semi-retractable current leads for a 21 T Fourier transform ion cyclotron resonance (FT-ICR) superconducting magnet system is presented. The semi-retractable current leads are composed of a normal metal element, conducting the current from room temperature to intermediate temperature, and an HTS element, conducting the current down to liquid helium temperature. An HTS element is partly immersed in liquid helium and the joint between the normal metal and HTS element is continuously refrigerated by a cryocooler. After magnet energization the metal element is disengaged from the HTS element without breaking vacuum to the insulating vacuum space. In the paper, the optimized dimensions of the leads are presented in order to minimize the thermal heat load when carrying operational current with some margin. The intermediate block with a lockable set point and the insulating vacuum system are fabricated and the adaptability and reliability are tested during engage and disengage performance. The effects of vacuum level and performance cycle on the electrical contact resistance in a lockable set are also investigated.

The inter-strand contact resistance (R(C)) of Nb(3)Sn cable-in-conduit conductors (CICCs) is a very important parameter which strongly correlates with ac losses and current redistribution behavior of the CICCs. One way to obtain the desired R(C) is to apply a layer of hydrocarbon oil on the Nb(3)Sn strands before the CICC Nb(3)Sn reaction heat treatment. In this paper, we measured R(C) for a Nb(3)Sn CICC sample fabricated with hydrocarbon oil. The measurements were performed using an apparatus designed to apply transverse load and load cycling on CICCs at 4.2 K. Resistances R(C) between strands of different cabling stages were measured with transverse load up to 188 kN m(-1) and load cycles up to 10 000. The results show that R(C) of the sample increases almost linearly with the first loading. With load cycling, R(C) increases rapidly at first, but becomes saturated after similar to 100 cycles. After 10 000 load cycles, R(C) decreases with increasing load at a decreasing rate. These behaviors are comparable to observations for CICC with Cr plated strands reported in the literature. Therefore from the R(C) point of view, Nb(3)Sn CICCs with hydrocarbon oil on strands may be used as a low cost alternative to CICCs with Cr plated strands.

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.

Cold rolled Cu-24 wt% Ag composite was characterized and the effects of crystallographic structure and defect anisotropy and microstructure refinement on properties of the composite were studied. Characterization was carried out with high resolution scanning electron microscopy (SEM), x-ray diffractometer and mechanical testing. All the deformed samples exhibited {110}-texture that had impact on the anisotropic properties of the materials. The yield and tensile strengths were higher in the long transverse (LT) than in the rolling direction (RD). The resistivity was higher in the RD than in the LT. Increasing the rolling strain increased both the mechanical strength and electric resistivity. The property changes with strain were related to the Cu and Ag lamellae thickness. The thickness of the lamella was inversely proportional to the deformation strain. It was observed that the smaller the thickness of the lamellae, the higher the strength and the electric resistivity. A closer examination of the Cu and Ag components revealed that while the lamellae were well aligned in the LT direction, they were curved in the RD. The curved lamellae observed in the RD were attributed to the development of shear bands during rolling. Both the texture and shear bands were related to the anisotropy of the properties.