Abstract
The rate, nu , of nucleation of vortices by negative ions in liquid helium under high pressures is calculated as a function of the electric field, E, applied to the ions. Measurements of nu (E) and nu (E), the drift velocity of ions, give sufficient information to determine the critical velocity required to form vortex rings and the rate at which these vortex rings are produced. This critical velocity is found to be 58.9+or-0.5 ms-1 for negative ions at 25 bar.