  The physical nature of the macroturbulence in the vortex matter in YBCO
superconductors is verified by means of magnetooptic study of the instability
in a single crystal prepared specially for this purpose. The instability
develops near those sample edges where the oppositely directed flow of vortices
and antivortices, guided by twin boundaries, is characterized by the
discontinuity of the tangential component of the hydrodynamic velocity. This
fact directly indicates that the macroturbulence is analogous to the
instability of fluid flow at a surface of a tangential velocity discontinuity
in classical hydrodynamics, and is related to the anisotropic flux motion in
the superconductor.
