A Study of Persistent Currents in Superfluid 4HE.
Abstract
Decay of saturated persistent currents in superleaks in contact with bulk superfluid helium has been studied using doppler shifts of the acoustic modes of an annular resonator partially packed with superleak. The two acoustic modes are an interpolated first-fourth sound and a modified second sound. Decay of such currents have been measured at 1.35 degrees K for annuli 10, 20, 40, 60, 80, 90, 95 and 100 percent filled with superleak. The main result which is somewhat surprising, is that the saturated persistent current and its fractional decay rate varies only slightly with superleak depth and the average decay rate is about 2.5% per decade. Another phenomena which was also studied is the doppler shift of gravity waves in a partially packed powder. The velocity of gravity waves is about three orders of magnitude smaller than the fourth sound velocity in a similar geometry. Thus it seemed appropriate to use its doppler shift for measuring small persistent currents. A theoretical study of the problem showed that the gravity waves are not doppler shifted in the presence of a persistent current in superleak, however the waves are still doppler shifted by the persistent currents in the free region. Experiments support the theoretical prediction, and also indicate the existence of a small current of about 8 millimeters per second in the free region. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1980
- Accession Number
- ADA085767
Entities
People
- Roset Khosropour Talaghany
Organizations
- University of California, Los Angeles