  Helium droplets produced by the instability of a cryogenic helium jet exiting
a source chamber leads to the formation of He drops which are considered as
ideal matrices for spectroscopic studies of embedded atoms and molecules. Here,
we present a He-DFT description of droplet formation resulting from jet
breaking and contraction of superfluid He-4 filaments. Whereas the
fragmentation of long jets closely follows the predictions of linear theory for
inviscid fluids, leading to droplet trains interspersed with smaller satellite
droplets, the contraction of filaments with an aspect ratio larger than a
threshold value leads to the nucleation of vortex rings which hinder their
breakup into droplets.
