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Quantum Turbulence in Superfluid 3 He-B at Ultra Low Temperatures.

Quantum Turbulence in Superfluid 3 He-B at Ultra Low Temperatures. D.I.Bradley D.O.Clubb S.N.Fisher A.M.Guenault. A.J.Hale R.P.Haley M.R.Lowe C.Mathhews. I.E.Miller M.G.Ward. G.R.Pickett R.Rahm K.Zaki. Introduction Vibrating Wires in superfluid 3He-B Observation of Turbulence

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Quantum Turbulence in Superfluid 3 He-B at Ultra Low Temperatures.

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  1. Quantum Turbulence in Superfluid 3He-B at Ultra Low Temperatures. D.I.Bradley D.O.Clubb S.N.Fisher A.M.Guenault A.J.Hale R.P.Haley M.R.Lowe C.Mathhews I.E.Miller M.G.Ward G.R.Pickett R.Rahm K.Zaki • Introduction • Vibrating Wires in superfluid 3He-B • Observation of Turbulence • The Spatial Extent of Turbulence • Direct measurements of Andreev scattering from Turbulence • Grid Turbulence

  2. 3He Phase Diagram Superfluid phases formed by Cooper pairs with S=1, L=1

  3. Vortices in the B-phase Formed by a 2p phase shift around the core superfluid flows around core with velocity, vS=k/2pr vortices are singly quantised with circulation : k=h/2m3 Superfluid is distorted in the core, core size depends on pressure: x0~ 65nm to 15nm

  4. Decrease in damping at higher temperatures implies that the damping from thermal quasiparticles is reduced. i.e. thermal quasiparticles are prevented from scattering with the detector wire.

  5. Quasiholes propagate through flow field

  6. Quasiparticles Andreev Scattered into Quasiholes with very small momentum transfer

  7. Fraction of flux Reflected =0.5*[1-exp(-pFv(r)/kBT)] v(r)=k/2pr, k=h/2m3 Shadow half Width = pFk/2pkBTln2 ~8mm@ 100mK (vortex core size x0 ~ 65nm @low P)

  8. Flow barrier independent of temperature below .22Tc

  9. Flow barrier decreases above .22Tc

  10. The heat input to the radiator (applied heat and heat leak) is balanced by a beam of ballistic quasiparticle excitations emitted from the radiator orifice.

  11. In the presence of vortices, the change in width parameter is proportional to the fraction of excitations Andreev reflected.

  12. Simple Estimate of vortex Line Density Take a thin slab of homogeneous vortex tangle of unit area, line density L and thicknessdx Mean qp energy =kBT Qps are Andreev scattered if pFv(r)> kBT v(r)=k/2pr, so qps scattered if they approach within a distance, r ~ kpF /2pkBT Probability of qp passing within distance r of a vortex core is L dx r Fraction of qps Andreev scattered after traveling dx through tangle, Ldx kpF /2pkBT Total fraction transmitted through tangle of thickness x is exp(-x/l), l~2pkBT/ LkpF

  13. Decay time of vortex tangle VWR measurements show the tangle disperses in ~ 3-4s From Simulations by C.F.Barenghi and D.C.Samuels, PRL 89 155302 (2002) Tangle disperses by evaporating small rings of size R~L-1/2 Rings form after a time t~1/(Lk) [~0.3s for our line densities] The tangle then expands at the self induced velocity of the rings, vR Time scale for tangle to disperse ~ S0/ vR ~5s for our line densities

  14. Grid Mesh: 11mm rectangular wires, 40mm square holes.

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