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A 25.05 T magnetic field was generated by a 5.11 T superconducting Bi2Sr2CaCu2Ox insert magnet within a 19.94 T resistive magnet. The Bi2Sr2CaCu2Ox magnet is constructed using fully reacted powder-in-tube conductor and insulated stainless steel reinforcement. Three concentric sections are used to minimize the total stress in the Bi2Sr2CaCu2Ox conductor: two double pancake stacks and an outer layer-wound section. The insert coil operates at 4.2 K in a 0.168 m diameter cryostat fitted to the resistive magnet. Here we provide an overview of the design and construction of the insert and the results of self-field and in-field testing. Mechanical and electrical safety issues, related to testing in a large resistive magnet, are discussed.

Sub-scale coils are being manufactured and tested at Lawrence Berkeley National Laboratory in order to develop wind-and-react Bi2Sr2CaCu20, (Bi-2212) magnet technology for future graded accelerator magnet use. Previous Bi-2212 coils showed significant leakage of the conductors' core constituents to the environment, which can occur during the partial melt reaction around 890 °C in pure oxygen. The main origin of the observed leakage is intrinsic leakage of the wires, and the issue is therefore being addressed at the wire manufacturing level. We report on further compatibility studies, and the performance of new sub-scale coils that were manufactured using improved conductors. These coils exhibit significantly reduced leakage, and carry currents that are about 70% of the witness wire critical current (/ c ). The coils demonstrate, for the first time, the feasibility of round wire Bi-2212 conductors for accelerator magnet technology use. Successful high temperature superconductor coil technology will enable the manufacture of graded accelerator magnets that can surpass the, already closely approached, intrinsic magnetic field limitations of Nb-based superconducting magnets.

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To evaluate the controlled quench behavior of high temperature superconducting (HTS) coils, particularly when using HTS coils in a hybrid configuration as an insert in a low temperature superconducting magnet, a layer-wound solenoid using Bi 2 Sr 2 CaCu 2 O wire was instrumented with several strip heaters to generate quenches in the axial and azimuthal directions. An array of distributed voltage taps and thermocouples were used to monitor the quench signals. Minimum quench energies (MQE) and quench propagation velocities (NZPVs) were determined. Results show that quench energies were moderate. NZPVs were slow but quench reaction times were of the same order as reaction times obtained at low quench energy densities in Nb 3 Sn coils.