The decay of quantum turbulence in superfluid (_^4)He in the zero temperature limit wasinvestigated. Quantum turbulence was created by impulsive spin-down from a specific angular velocity to rest. A measurement of the vortex line density was performed using the scattering of charged vortex rings. The vortex line density decayed as L ? t^(-3/2) which is the characteristic of quasiclassical turbulence forced at large length scales. The interaction of metastable spin-triplet ?He?_2^* molecules with quantized vortex lines in superfluid (_^4)He at temperatures below 200 mK was studied too. The molecules were generated during an injection of electrons from a sharp metal tip at high voltage. They were detected as a current into a metal collector after ionization upon colliding with the collector surface. The detected current was suppressed by even a small rotation indicating the trapping of the molecules on quantized vortices. The presence of (_^3)He impurities at the level of 0.3 ppb strongly suppressed the detected signal. The temperature dependence of the detected signal showed a sharp peak, most probably associated with the condensation of (_^3)He atoms on vortex cores. The time of flight of the molecules as a function of temperature was measured. It was observed that there are three regimes for ?He?_2^* molecules transportation in superfluid (_^4)He : ballistic regime for T 200 mK, and an intermediate regime between them. The vortex lines were created by either rotation or ion injection. The trapping diameter of the molecules on quantized vortices was found to be 96 � 6 nm at pressure of 0.1 bar and 27 � 5 nm at 5.0 bar. It was also demonstrated that a tangle of vortices moving in superfluid (_^4)He are capable of conveying the ?He?_2^* molecules through the drift region.The decay of quantum turbulence in superfluid (_^4)He in the zero temperature limit wasinvestigated. Quantum turbulence was created by impulsive spin-down from a specific angular velocity to rest. A measurement of the vortex line density was performed using the scattering of charged vortex rings. The vortex line density decayed as L ? t^(-3/2) which is the characteristic of quasiclassical turbulence forced at large length scales. The interaction of metastable spin-triplet ?He?_2^* molecules with quantized vortex lines in superfluid (_^4)He at temperatures below 200 mK was studied too. The molecules were generated during an injection of electrons from a sharp metal tip at high voltage. They were detected as a current into a metal collector after ionization upon colliding with the collector surface. The detected current was suppressed by even a small rotation indicating the trapping of the molecules on quantized vortices. The presence of (_^3)He impurities at the level of 0.3 ppb strongly suppressed the detected signal. The temperature dependence of the detected signal showed a sharp peak, most probably associated with the condensation of (_^3)He atoms on vortex cores. The time of flight of the molecules as a function of temperature was measured. It was observed that there are three regimes for ?He?_2^* molecules transportation in superfluid (_^4)He : ballistic regime for T 200 mK, and an intermediate regime between them. The vortex lines were created by either rotation or ion injection. The trapping diameter of the molecules on quantized vortices was found to be 96 � 6 nm at pressure of 0.1 bar and 27 � 5 nm at 5.0 bar. It was also demonstrated that a tangle of vortices moving in superfluid (_^4)He are capable of conveying the ?He?_2^* molecules through the drift region.

Sep 24, 20140 citations

Ions in Superfluid He4

Tao Pang

Physical Review LettersOct 10, 19881 citation

INTERACTION OF IONS WITH VORTEX LINES

A. F. Borghesani

Abstract If the superfluid is contained in a rotating bucket, it resembles a solid-body rotation by developing an uniform array of quantized vortex lines. These can capture ions and, thus, rotating superfluid He II shows a strong anisotropy to the motion of ions. This chapter is concerned with the interaction of ions with vortex lines. The ion capture experiments and their results are described. Concepts such as capture width are discussed. A theoretical model of Brownian diffusion has been developed to understand the capture of ions by vortex lines. The competition between the attractive hydrodynamic suction and the thermal diffusion leads to an effective capture rate of ions. The effect of the pressure on the capture of an electron bubble is also discussed.Abstract If the superfluid is contained in a rotating bucket, it resembles a solid-body rotation by developing an uniform array of quantized vortex lines. These can capture ions and, thus, rotating superfluid He II shows a strong anisotropy to the motion of ions. This chapter is concerned with the interaction of ions with vortex lines. The ion capture experiments and their results are described. Concepts such as capture width are discussed. A theoretical model of Brownian diffusion has been developed to understand the capture of ions by vortex lines. The competition between the attractive hydrodynamic suction and the thermal diffusion leads to an effective capture rate of ions. The effect of the pressure on the capture of an electron bubble is also discussed.

May 31, 20071 citation

Stochastic theory of the interaction of ions and quantized vortices in helium II

Russell James Donnelly, Paul Harry Roberts

Abstract The interaction of ions and quantized vortex lines in helium II is treated by imagining that the motion of the superfluid near a vortex line acts on an ion so as to produce a potential well. The ion itself is looked upon as a Brownian particle immersed in a gas of quasi-particles. The capture of ions is pictured as a process of sedimentation into the well. The escape of the ions from the well is treated as a problem of the escape of a Brownian particle over a potential barrier. A solution of the Fokker-Planck equation for a two-dimensional well is given. Comparison of the theory with a variety of experiments is presented.Abstract The interaction of ions and quantized vortex lines in helium II is treated by imagining that the motion of the superfluid near a vortex line acts on an ion so as to produce a potential well. The ion itself is looked upon as a Brownian particle immersed in a gas of quasi-particles. The capture of ions is pictured as a process of sedimentation into the well. The escape of the ions from the well is treated as a problem of the escape of a Brownian particle over a potential barrier. A solution of the Fokker-Planck equation for a two-dimensional well is given. Comparison of the theory with a variety of experiments is presented.

Proceedings of the Royal Society of London A Mathematical and Physical SciencesSep 30, 1969113 citations

Interaction of Ions, Atoms and Small Molecules with Quantized Vortex Lines in Superfluid

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