Dissipation in the Flow ofHe3-Aand

Abstract

Measurements are reported which relate to the dissipation and superfluid density of 3 Ue-A and 3 He-i3 flowing through a long rectangular channel of cross section 48 nm x 2.86 mm at currents between 5x io" 2 g cm" 2 sec" 1 and 5>< 10" 5 g cm" 2 sec" 1 and at temperatures down to T/T c = 0.52. The results show a complex velocity dependence in both phases.PACS numbers: 67.50.Fi Several reported flow observations on superfluid 3 He are consistent with a two-fluid model in which the viscosity of one component is small or zero up to a critical velocity where dissipation sets in. 1 " 3 In this paper we report new measurements on the superfluid phases of 3 He in undirectional and oscillatory flow of frequency 0-40 Hz through a narrow rectangular channel of cross section approximately 48 /im (between polished faces)x2.86 mm and length 9.16 mm at temperatures down to T/T c = 0.52. The special characteristics of our experiments are a high sensitivity to dissipation, a wide range of driven flow currents, and direct observation of flow. These characteristics have enabled us to observe many new phenomena: most notably, in 3

Spin pump for boosting spin polarization of superfluidHe3A1phase

“…3, where and ⌬Z͑t =20 s͒ approach their limiting values in the N phase, is likely related to such an effect but is not well understood. 20 When the imposed diaphragm velocity is reduced in a separate temperature sweep run, T x is found to increase as expected. The critical current estimated from Ż at t =15 s, r = 0.5, and s / ϳ 0.01 ͑Ref.…”

“…2 is ϳ1 ϫ 10 −3 g / cm 2 s. This critical current is smaller than the reported 22 pair-breaking current in the superfluid 3 He B phase but falls in the range found by others. 20 The spin pressure cannot simply be extracted via Eq. ͑1͒ from Z͑t͒ where dissipative effects set in at T տ T x .…”

Superfluid Dissipation in RotatingHe3-B

“…This dissipation increases linearly with angular velocity. Similar dissipation in rotating 4 He is attributed to mutual friction between quasiparticles and quantized vortex lines. 3 Using the same model of mutual friction as in 4 He, we find the mutual friction coefficient in 3 He to be roughly a factor of 2 larger.…”

“…In the case of superfluid 4 He the well-known quantized vortex lines appear in the rotating superfluid. Similar, but more complex, vortex structures are expected in 3 He-A and -B, and recent NMR experiments 2 have already provided some evidence for their existence.…”

“…This geometry avoids the junctions from narrow flow channels to open volumes of helium that were present in earlier experiments. 4 The fill line enters at the center of the folded slab, so that it is at a pressure node of the oscillatory flow.…”