High performance stabilization in superfluid helium

We present measurements of the critical angular velocity for the onset of vorticity in a rotating annulus. The measurements of the critical velocity were made over a temperature range from 1.5 to 2.165 K, and are consistently lower than theoretical predictions by about 20%. Nor do our results agree within experimental uncertainty with previous measurements of the critical velocity in an annulus. It appears that the discrepancies can be explained by the presence and growth of high concentrations of residual vorticity which prevent the system from achieving the lowest free energy state. We find that vorticity perpendicular to the axis of rotation grows as the angular velocity is increased and that the axial mutual friction coefficient B" is O.

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Frequency-crossing phonon spectrometer techniques

Wybourne

Jefferies

Challis

et al. 1979

Review of Scientific Instruments

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An ac technique for measuring magnetothermal conductivities using frequency crossing has been developed and shows a 13-fold increase in signal-to-noise ratio over the conventional dc technique. The ac technique employs low-frequency field modulation coupled with phase-sensitive detection and a 45-fold improvement in signal-to-noise ratio may be obtained by modulation over the half-width of the frequency crossing signal. A further increase of approximately 3 would be obtainable by increasing the modulation frequency and overcoming technical problems. The limit of detection and instrument revolution may be as low as 10 in. spins and a few megahertz, respectively.

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High performance stabilization in superfluid helium

Cited by 5 publications

References 4 publications

Control of Pressurized Superfluid Helium-II: Application to Loss Analysis

Control of Pressurized Superfluid Helium-II: Application to Loss Analysis

Onset of vorticity in a rotating annulus of helium II

Frequency-crossing phonon spectrometer techniques

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