Persistent currents in a rotating superleak partially filled with superfluid helium
Persistent currents in a partially helium II filled rotating superleak have been investigated. Measurements were made using the acoustic doppler shift of the thickness wave in the helium II film which covers the alumina powder grains (1 micron) of the superleak. The superleak is contained in an annular resonator. Q's as high as 120 were observed. The acoustic index of refraction, n, has been measured as a function of filling fraction, f (f is the fraction of pores filled with liquid He II). Motivated by a model which treats the scattering from the powder and vapor separately an expression for the index of refraction, n, has been formulated. The data is in excellent agreement with this formulation for 0.3 < f < 1.0. When f = 1 the system becomes a fourth sound resonator and the value of n is in excellent (1%) agreement with that from fourth sound. The existence of a potential flow region (Landau region) was established and measured at low rotational speeds (below 0.5 Hz). This region is comparable to the Meissner region in irreversible high field type-II superconductors. The upper bound on this region Wc1 plays the same role as Hc1 does in the type-II superconductor. At rotational velocities greater than Wc1 quantized vortices enter the system. These vortex lines are directly comparable to quantized magnetic flux lines in type-II superconductors. At even higher rotational velocities w/sub s/ - w/sub s/ becomes a maximum at a rotational velocity Wsig. The dependence of wsigma (about 1 Hz) was measured as a function of temperature and filling fraction.
- Research Organization:
- California Univ., Los Angeles (USA)
- OSTI ID:
- 5121253
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACOUSTIC MEASUREMENTS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CURRENTS
DATA
DOPPLER EFFECT
ELECTRONIC EQUIPMENT
EQUIPMENT
EVEN-EVEN NUCLEI
EXPERIMENTAL DATA
FILMS
FLUID FLOW
FLUIDS
HELIUM 4
HELIUM II
HELIUM ISOTOPES
INFORMATION
ISOTOPES
LIGHT NUCLEI
MOTION
NUCLEI
NUMERICAL DATA
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POWDERS
QUANTUM FLUIDS
REFRACTIVITY
RESONATORS
ROTATION
SCATTERING
STABLE ISOTOPES
SUPERFLUIDITY
TEMPERATURE DEPENDENCE
VELOCITY