Research:

Low-Temperature Experimental Physics and Applied Physics, including SQUID-based magnetic measurement, low-temperature magnetic detectors, superfluid helium, magnetic thermometry, and cooling technology.

Research Topics

Low-Temperature Magnetic Detectors

Current research in collaboration with STAR Cryoelectronics. Shown here is the new layout for the miniature SQUID-based magnetic gradiometer with integral magnetizing field coils and persistence switch. This device will be used to study the temperature-dependent magnetization of very small samples ~50 micron. Pads for the electrical connections to the SQUID are on the right. The two large pads on the left are for the two spiral magnetizing field coils located in the middle of the chip, one centered over each pickup loop. The smaller pads on the left are for the persistence switch. The enlargement on the right shows a ~50u dia sample loaded into a pickup coil.

Recent Stuff:

• Microcalorimeter magnetic sensor geometries using superconducting elements, S. T. P. Boyd, R. H. Cantor, presented at the 13th International Workshop on Low Temperature Detectors, Stanford, July 20-24, 2009, proceedings to be published in J. Low Temp. Phys. pdf preprint (849.63 Kb)
• Miniature Thin-Film SQUID Susceptometer for Magnetic Microcalorimetry and Thermometry, S. T. P. Boyd, Vincent Kotsubo, Robin Cantor, Alexander Theodorou, and J. Ad Hall, IEEE Transactions on Applied Superconductivity, 19 (3), 697-701, (June 2009), selected for early online publication in the European Superconductivity News Forum, available at: http://www.ewh.ieee.org/tc/csc/europe/newsforum/pdf/Boyd_2EPE02.pdf).
• Characterization of a miniature thin-film SQUID susceptometer for metallic magnetic microcalorimetry, S.T.P. Boyd, R. Cantor, V. Kotsubo, P. Blumenfeld, J.A. Hall, J. Low Temp. Phys. 151, 369 (2008).
• Miniature Thin-Film Superconducting Quantum Interference Device Susceptometer, Robin Cantor, J. Ad Hall, Phil Blumenfeld, and Stephen T. P. Boyd, IEEE Transactions on Applied Superconductivity 17 (2), 738 (2007).

Properties of Helium-4 Near its Superfluid Transition

In 4He very near the Lambda Transition, when a uniform heat flux is directed downwards, parallel to the force of gravity, the divergent thermal resistivity of the helium allows it to self-organize into a state ("SOC") in which the temperature profile exactly follows the pressure-induced variation of T_lambda, plus a small offset which is determined by the heat flux magnitude. This highly nonlinear thermal system supports a temperature wave which propagates upwards only. We are currently analyzing the last of the data obtained by the sidewall-thermometry "DYNAMX" experiment (PI: Rob Duncan), which has the highest heat flux and AC drive levels ever observed for the SOC.

Recent Stuff:

• Effect of Inhomogeneous Heat Flow on the Enhancement of Heat Capacity in Helium-II by Counterflow near Tλ, STP Boyd, AR Chatto, RAM Lee, RV Duncan, and DL Goodstein, Proceedings of the 24th International Conference on Low Temperature Physics, AIP Conference. Proceedings. 850, 133 (2006).
• CW Measurement of the Upward-Going Temperature Wave in the Helium-4 Self-Organized Critical State, STP Boyd, DA Sergatskov, and RV Duncan, Proceedings of the 24th International Conference on Low Temperature Physics, AIP Conference Proceedings 850, 135 (2006).

Teaching

......Current MATLAB Class

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