Physical Review Letters

Vortex-Ring Formation by Negative Ions in He ii Under Pressure

Donald A. Neeper

Published Jul 29, 1968• 41 citations

Abstract

It was previously shown that at temperatures \ensuremath{\ge}0.36\ifmmode^\circ\else\textdegree\fi{}K and pressures >12 atm negative ions in He II could be accelerated until they emitted rotons at velocities of about 50 m/sec. We find that at temperatures \ensuremath{\le}0.3\ifmmode^\circ\else\textdegree\fi{}K negative ions produce only vortex rings at pressures up to 16 atm.

DOI: 10.1103/physrevlett.21.274

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Physical Review Letters

Vortex-Ring Formation by Negative Ions in He ii Under Pressure

Donald A. Neeper

Published Jul 29, 1968• 41 citations

Publisher

Abstract

DOI: 10.1103/physrevlett.21.274

Related papers

Vortex-Ring Creation by Negative Ions in Dilute Mixtures of He3 - He4

George W. Rayfield

We describe an experiment which indicates that the addition of ${\mathrm{He}}^{3}$ impurities to superfluid helium has a pronounced effect on the velocity at which negative ions produce vorticity (vortex rings). The ${\mathrm{He}}^{3}$ impurities have no effect, however, on the creation of vorticity by positive ions.We describe an experiment which indicates that the addition of ${\mathrm{He}}^{3}$ impurities to superfluid helium has a pronounced effect on the velocity at which negative ions produce vorticity (vortex rings). The ${\mathrm{He}}^{3}$ impurities have no effect, however, on the creation of vorticity by positive ions.

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We describe an experiment which indicates that the addition of

{\mathrm{He}}^{3}

impurities to superfluid helium has a pronounced effect on the velocity at which negative ions produce vorticity (vortex rings). The

{\mathrm{He}}^{3}

impurities have no effect, however, on the creation of vorticity by positive ions.

We have measured the drift velocity

\overline{v}

of negative ions through superfluid

^{4}\mathrm{He}

for temperatures

T<0.45

K, under a pressure of 25 bar, for electric fields $20<E<2.6\ifmmode\times\else\texttimes\fi{}{10}^{4}$ V ${\mathrm{cm}}^{\ensuremath{-}1}$. From the observed form of

\overline{v}(E)

, we deduce that roton emission from an ion traveling faster than the Landau critical velocity is governed by hitherto unrecognized selection rules whereby the rotons can be created only in pairs.

\frac{\mathrm{dP}}{\mathrm{dT}}

and positive second derivatives

\frac{{d}^{2}P}{d{T}^{2}}

. The results have been interpreted in terms of the bubble model of the negative ion and the vortex-line model of the rotating superfluid. The interpretation suggests that the ion radius equals approximately 19.5 A at saturated vapor pressure and decreases to a value between 12 and 14 \AA{} at the solidification pressure. However, a significant discrepancy between theory and experiment casts some doubt on the radius values obtained.