Quenching of the Ion/Vortex-Ring Transition in He II by Intense Electric Fields

The rate $\nu$ at which negative ions nucleate charged vortex rings in isotopically pure superfluid helium-4 has been measured for electric fields of up to 2.5×${10}^6$ V ${\mathrm{m}}^{-1\mathrm{}}$ with pressures and temperatures within $17<P<\mathrm{}25\mathrm{}$ bars, $0.3<T<\mathrm{}0.9\mathrm{}$ K. It is found that the nucleation process is completely quenched ($\nu =0\mathrm{}$) for $E>\mathrm{}2\mathrm{}\times {10}^6$ V ${\mathrm{m}}^{-1\mathrm{}}$. The implications of this result for theories of the nucleation mechanism are discussed.