High Field REBCO Research Articles

Protection Heater Development for REBCO Coils

Normal zone propagation rates are widely reported to be low in coils containing REBCO coated conductor, creating difficulties for quench protection of high field REBCO insert solenoids. A method of active quench protection using densely distributed heaters in high field REBCO coils has been proposed. When heaters are used to quench a sufficiently large fraction of the coil windings, the hot-spot temperature can be limited to acceptable values. The feasibility of protection of REBCO coils by distributed heaters depends on the amount of power to quench the required fraction of the coil volume, and the ability of the heaters to quench REBCO coils quickly. The high critical temperature of REBCO compared to low-temperature superconductor implies that the windings must be elevated significantly higher in temperature to initiate a normal zone. A number of measurements have been made of the performance of protection heaters on REBCO high field test coils. The results provide information on the response of coils to active protection heaters. Typically, there is a delay between the activation of the heater and the onset of quench in a coil. Measurements give the relation between the heater power and the quench delay time.

Design of a Superconducting 32 T Magnet With REBCO High Field Coils

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.