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

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.