Speaker
Description
Princeton Plasma Physics Laboratory is advancing the development of large-bore, high-field, high-temperature superconducting (HTS) magnets to support cutting-edge physics research at Princeton University (PU). A 3-phase REBCO magnet program was initiated to address critical challenges and develop essential technologies for HTS magnet development. In Phase 1, we established the HTS research infrastructure through building a compact REBCO coil. Phase 2 focuses on validating key techniques in stress management and quench mitigation through developing a high-field prototype REBCO insert magnet. Phase 3 aims to deliver a full-scale, high-field user magnet capable of housing a state-of-the-art scanning tunneling microscope at PU.
Here, we present the progress in Phase 2, detailing the design, fabrication, and standalone testing of the prototype REBCO insert magnet. The prototype features a 72-mm cold bore and is designed to generate at least an 8-T field within a 12-T background, achieving a combined 20-T magnetic field. The magnet comprises 21 "metal-insulation (MI)" double-pancake (DP) coils, each wound with 4-mm wide, 75-µm thick REBCO tape, parallel with 50-µm thick 316 stainless steel (SS) tapes. To enhance structural integrity, an SS overband with a 6-mm radial build is applied to all DPs. The dry-wound MI approach offers several advantages, including a high conductor current density, enhanced structural stiffness, and compact dimensions suitable for nesting with a 160-mm-bore low-temperature superconducting outsert. Numerical analyses confirm that the structural design can support the insert magnet in achieving up to 12-T field within a 12-T outsert, accounting for the screening current effect. Initial testing is conducted in liquid nitrogen (65–77 K) for quality assurance, followed by standalone testing in liquid helium (4.2 K). Detailed approaches for quench detection and protection are presented, including voltage-based quench detection, minimizing inductive signal through voltage differences between symmetrically positioned coils. Additional strategies involve employing the SS overband as part of the dump resistor for efficient energy dissipation and incorporating surface shunts to enhance inter-turn current sharing. The quench-associated magnetic coupling behaviors are also discussed.
