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To explore the limits of layer wound (RE)Ba 2 Cu 3 O 7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment > 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.The cuprate based high temperature superconductor (RE)Ba 2 Cu 3 O 7-x (REBCO, RE = Rare Earth), has the capability to substantially transform the technology of high field magnet systems. So far, the low temperature superconductors Nb-Ti and Nb 3 Sn have been used for virtually all superconducting high field magnets. Their maximum field, however, is limited by their upper critical fields (H c2 ) of about 15 T for Nb-Ti and 30 T for Nb 3 Sn, which limits their highest practical field to about 23.5 T 1 . This limit is imposed by the rapid decrease in critical current density J c as H c2 is approached. By contrast, REBCO has an H c2 that exceeds 100 T at 4.2 K, removing the H c2 and J c limit that restricts usage of Nb 3 Sn in highfield magnet systems. One of the goals at the NHMFL is to develop the necessary technology for the next generation of high-field magnets including Nuclear Magnetic Resonance (NMR) quality magnets. To reduce the number of resistive joints and achieve the required field homogeneity for NMR, layer-winding

The design and fabrication of a 32 T, 32 mm cold bore superconducting magnet with high field REBCO inner coils is underway at the NHMFL. In support of the design, conductor characterization measurements have been made including critical current as a function of field, field orientation, temperature, and strain on conductors and joints. Various conductor and turn insulation systems were examined. The selected coil fabrication method for the 32 T magnet is pancake wind, dry wind coils with sol-gel insulation on a stainless steel co-wind. Quench protection of the REBCO coils by distributed heaters is under development. Small REBCO coils have been made and tested in a 20 T background field to demonstrate performance of the technology. The design of the 32 T magnet is described, including coil configuration and conductor lengths, fraction of critical current, selection of conductor copper content for protection, and stress in the windings.Index Terms-High field superconducting magnets, insulation, quench protection, REBCO.

A superconducting dipole, designed for use as a sweeper magnet in nuclear physics experiments, has been designed and built by the National High Magnetic Field Laboratory for operation at the National Superconducting Cyclotron Laboratory. The magnet operates at a peak field of 3.8 T in a 140 mm gap. A secondary beam enters the magnet from the upstream side before striking a target. The neutrons continue straight through to a neutron detector. The charged particles are swept 40 degrees on a one-meter radius into a particle spectrometer. To allow space for the exit of the downstream neutron beam, the magnet iron and coil structure are built in a modified "C" configuration. There are two coils of "D" shape, one above and one below the beam. This configuration keeps the magnet compact and removes the need for a negative curvature side. The peak field in the winding is 6.5 T. The net force on the curved leg of a single "D" is 1.6 MN. Results of system testing including cool-down, quench history, and integration with the cyclotron are presented.

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The next generation of high-field magnets that will operate at magnetic fields substantially above 20 T, or at temperatures substantially above 4.2 K, requires high-temperature superconductors (HTS). Conductor on round core (CORC) cables, in which RE-Ba 2 Cu 3 O 7−δ (RE = rare earth) (REBCO) coated conductors are wound in a helical fashion on a flexible core, are a practical and versatile HTS cable option for low-inductance, high-field magnets. We performed the first tests of CORC magnet cables in liquid helium in magnetic fields of up to 20 T. A record critical current I c of 5021 A was measured at 4.2 K and 19 T. In a cable with an outer diameter of 7.5 mm, this value corresponds to an engineering current density J e of 114 A mm −2 , the highest J e ever reported for a superconducting cable at such high magnetic fields. Additionally, the first magnet wound from an HTS cable was constructed from a 6 m-long CORC cable. The 12-turn, double-layer magnet had an inner diameter of 9 cm and was tested in a magnetic field of 20 T, at which it had an I c of 1966 A. The cables were quenched repetitively without degradation during the measurements, demonstrating the feasibility of HTS CORC cables for use in high-field magnet applications.