Scott Gundlach

Progress in the Development of a Superconducting 32 T Magnet With REBCO High Field Coils

The design and development of a 32 T, 32 mm cold bore superconducting magnet with high field REBCO inner coils are underway at the NHMFL. The two nested REBCO coils that form the high field section are dry wound, with uninsulated conductor and insulated stainless steel cowind reinforcement. Active quench protection uses distributed protection heaters. As part of the development activity, prototype coils of the two REBCO coils with full scale radial dimensions and final design features, but with reduced axial length are being constructed. The first of these prototype coils was tested in a 15 T resistive background field magnet. The coil has inner and outer winding diameters of 40 mm and 140 mm, respectively, and consists of six double pancakes with a total conductor length of roughly 900 m. The construction of this prototype coil is described, including the protection heaters. Coil test results are reported including coil critical current, coil ramping characteristics, thermal stability, joint, and terminal resistance with field cycling. The corresponding operating stress in the windings is calculated. Importantly, the performance characteristics of the protection heaters will be measured including activation time.

Progress in the Development and Construction of a 32-T Superconducting Magnet

The 32-T superconducting magnet is envisioned as a 15-T low-temperature superconductor (LTS) magnet combined with a separately powered REBCO high-temperature superconductor (HTS) insert configured as two coil stacks generating 17 T. Progress was made in all aspects of this project and is reported in this work. The design concept, which has been quite stable, is presented, as well as key elements from recent developments such as increased voltage standoff requirements. In both factory testing and installation at the NHMFL, the 15-T/250-mm-bore outer magnet built by Oxford Instruments met all specifications, including a ramp time of 1 h to full field. The test protocol included a deliberately induced full-field quench, releasing 7 MJ. After the helium level recovered, the magnet was ramped again in 1 h to full field, demonstrating full recovery. Helium boiloffs during normal operation and quench were observed, as well as the current and field decay during quench. The latter information serves as one of many inputs for the numerical quench code developed specifically to model quench in coupled LTS-HTS coils. Results from the 32-T quench analysis and implications for quench protection are summarized. All HTS conductor lengths were subjected to an extensive quality assurance (QA) protocol, and SuperPower has now delivered all required conductor lengths within specifications. A summary of the QA data and its implications are presented. The prototype coils, which are very similar in design to the 32-T REBCO coils but of reduced height, have now been impregnated with paraffin to address winding motion observed in previous testing. The prototype test protocol includes a study of the effectiveness of the quench heaters in the HTS coils in both a constant background field as provided by the actual 15-T LTS outer magnet for 32 T and, uniquely, in case the outer magnet is deliberately quenched.

The Powered Scattering-Magnet Program at the NHMFL

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.

Conceptual Design of Powered Scattering Magnets at the NHMFL

The NHMFL is developing conceptual designs of powered magnets with novel configurations. Conical hybrid magnets are being considered using a novel Conical Florida-Bitter technique. A resistive split magnet is being developed and will be installed at the powered magnet facility in Tallahassee. This magnet will be used for scattering experiments with far-infrared light as well as rotation experiments

Sol-gel-Derived

Electrically insulating Al2O3-SiO2 thin coatings have been deposited on long-length 316 stainless steel (SS) tape using a reel-to-reel continuous solgel dip coating process for cowinding insulation into YBCO pancake coils, a high-temperature superconductor magnet technology. Coatings with a thickness of ~ 5 μm are achieved after just two dips with a tape withdrawal speed of ~ 8 mm/s (0.5 m/min) and a calcination at 700 °C. The coatings are measured to have a room-temperature breakdown voltage of ~ 200 V, corresponding to a dc dielectric strength of about 40 MV/m. Consequently, this process has low cost and high throughput and produces a thin electrical insulation with excellent thermal, dielectric, and mechanical properties. A new technique has been developed in the coating process to mitigate Al2O3 particulate aggregation and coating buildup along the edges of the SS tape.

\hbox{Al}_{2}\hbox{O}_{3}{-} \hbox{SiO}_{2}

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.

Composite Coating for Electrical Insulation in HTS Magnet Technology

The National High Magnetic Field Laboratory in Tallahassee, Florida, USA has designed, built and tested a high field, split pair, Repetitively Pulsed Magnet (RPM) suitable for neutron scattering experiments. RPM magnets have the advantage of lower average power and lower construction costs than DC magnets. The NHMFL RPM program intends to build magnets with higher field and larger scattering space than those available elsewhere. Details of design and testing of the first prototype are presented

Resistive Solenoid Development at the NHMFL

The HTS insert for the 32 T superconducting magnet is comprised of two dry wound, double pancake REBCO coils of different lengths, nested within an LTS outsert. The high fields present within the HTS coils create large axial compression forces and significant radial expansion. The mechanical solutions implemented to account for the effects of axial and radial coil movement are described. These solutions are applied throughout many of the mechanical subsystems in and between the HTS coils, including electrical terminations, electrical bussing, external reinforcing of the windings, and suspension of the HTS coils within the outsert. Experiences from the assembly in preparation for the initial operation of the magnet are also shared.

Design a Testing of a Repetitively Pulsed Magnet for Neutron Scattering

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.