Annihilation of vortex lines in rotating superfluid 3He

In decelerating rotation, vortex lines annihilate in single-vortex events at the annihilation threshold where their number Nmax(Ω) is equal to or exceeds the equilibrium value Neq(Ω). A surplus Nmax-Neq may be stabilized by an energy barrier, which during deceleration vanishes in an instability. We find the barrier to depend on container misalignment in 3He-B and on the orbital texture in the container corners in 3He-A. Measurements of the instability yield the circulation quantum of the vortex which is found to be consistent with the present identification of vortex structures in 3He-A. copyright 1997 The American Physical Society