Evolution of vortex rings after the collapse of ultrasound bubbles in superfluids

Collapse of ultrasound bubbles in superfluids leads to the nucleation of vortex rings. Using the Gross-Pitaevskii equation for a uniform condensate we elucidate the various stages of the vortex formation and establish conditions necessary for the vortex nucleation after the collapse of an oblate moving bubble. In the case of a stationary spherically symmetrical bubble we calculate the vortex line length as a function of time after collapse.