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A Thermally Actuated Flux Pump for Energizing YBCO Pucks
DST Group Edinburgh Edinburgh SA Australia
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This paper presents results for the magnetization of a disc of YBCO by sending heat pulses through a disc of dysprosium below it. As the heat pulses move through the dysprosium its magnetic properties change producing a wave of magnetization across the disc of YBCO. This wave of magnetization sweeps vortices into the YBCO and each subsequent wave sweeps in more vortices, gradually increasing the magnetization of the YBCO. The YBCO disc was 30 mm in diameter and 15 mm high and the dysprosium was 30 mm in diameter and 13 mm high. The dysprosium undergoes a change from ferromagnetic to anti-ferromagnetic as it passes through a temperature of 85 K so the temperature range of the heat pulses went from below this temperature to a temperature above it. The dysprosium and YBCO were connected into an iron magnetic circuit to create a low reluctance path with three copper coils on parts of the circuit. Currents through the coils generated flux in the magnetic circuit. The circuit was cooled using a cryocooler and heat pulses were applied to the dysprosium by turning the cold head on and off. These heat pulses varied the temperature of the dysprosium above and below the ferromagnetic anti-ferromagnetic transition, sweeping vortices into the YBCO causing a magnetic field to gradually accumulate. It was found that the field initially grew to a certain level and then stayed constant no matter how long the pulses were applied. The pattern was found to be the same for four different coil currents and therefore two different starting values for the flux in the circuit.
APPROVED FOR PUBLIC RELEASE