The effect of strong electric fields on exotic negative ions in He II: Possible evidence for the nucleation of charged vortex rings

Abstract

We present evidence suggesting that Ihas and Sanders' intermediate mobility exotic negative ions can nucleate quantised vortex rings in superfluid 4He when subjected to strong enough electric fields.Several years ago, Doake and Gribbon discovered [1] that there can exist in He II a fast ion which, unlike the normal negative ion [2], may be accelerated to the Landau critical velocity v L for roton creation without undergoing metamorphosis to a charged vortex ring, even under the saturated vapour pressure. Although Doake and Gribbon were unable to ascertain the physical conditions needed to generate this mysterious entity reproducibly, Ihas and Sanders showed [3,4] soon afterwards that the vital factor apparently lay in the provision of an electrical discharge in the vapour above the surface of the liquid. The latter authors also discovered that the glow discharge source produces not only the normal and fast negative ions, but also (astonishingly) a large number of other types of negative ion with low-field mobilities lying intermediate between those of the fast and normal ions.The existence of this unexpected plethora of exotic negative charge carriers in He II constitutes an intriguing and still unsolved theoretical problem. Although the structure of the normal negative ion is understood in considerable detail [2] the nature(s) of the fast *

Electrons in Liquid Helium

“…[44][45][46] They, too, detected the fast ion and several of the exotic ions with different mobilities. In their measurements, the mobility in large electric fields was studied, whereas IS had investigated the mobility in low fields.…”

Motion of electrons in liquidH4e

“…In Ref. 5 their behavior has been tentatively attributed to a motion of an electron bubble undergoing a continuous sequence of escape-trapping-escape events of charged vortex rings.…”

“…3,4 Both fast and exotic ions under high electric fields have been studied in Ref. 5, where they found that the fast ions can reach the Landau critical velocity v L while the exotic ions decay instead into charged vortex rings before being able to reach v L .…”

Exotic Self-trapped States of an Electron in Superfluid Helium

“…Now the electron is liberated and free to be recaptured by vorticity elsewhere in the helium. Thus, while a decayingexponential drift velocity is consistent with the high field measurements of Eden and McClintock [11], the low field mobility would appear to lack the robust characteristics recently established by Maris and coworkers [1]. The most promising scenario then, of electron-vortex-bound states as the elusive fast and exotic ions, is for the electron to establish an equilibrium structure.…”