Motion of ions, trapped on vortex lines in superfluid 4He

Abstract

The dynamics of vortex lines in superfluid 4He were probed in this experiment by briefly applying an electric force on electrons, self-localized in microscopic bubbles in liquid helium. The electron bubbles were trapped by straight vortex lines which were formed in the rotating superfluid at temperatures between 0.1 K and 0.8 K. The goal was to investigate the conditions for a kink wave, called soliton, with a trapped electron bubble to be converted into a charged vortex ring (CVR) following a self-reconnection of a vortex line. Vortex rings are one of the main structures that are observed in quantum turbulence (QT). They play an important role in transporting energy and momentum in QT. Therefore, their formation and motion can give insights into the dynamics of vortex lines and turbulence in superfluid 4He. The trapped electron bubbles were initially confined by an electrostatic trap of length ~ 1 cm, located at distance 3 cm from the collector, with typical spacing of ~ 0.1 - 0.4 um on a vortex line. Then they were pulled along the vortex line by a parallel force due to an electric field of chosen magnitude in the range 17 - 50 V/cm and duration between 2 ms and 0.5 s. As a result, a fraction of electron bubbles arrived at the collector in time ~ 3 ms with a limiting velocity of ~ 10 m/s. The rest detached from rectilinear vortex lines and formed singly-charged CVRs of a small initial radius R_0. By analysing the shape of the collector current peak I_c(t) due to CVRs, at times between t = 0.1 s and t = 1 s, the distribution of R_0 was determined to be between 0.15 um and 1.4 um, and the initial location of trapped electron bubbles that resulted in CVRs to be between 0 and ~ 6 mm from the centre of the electrostatic trap.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrei Golov (Supervisor) & Paul Walmsley (Supervisor)