Vortex flow in rotating superfluid 3He-B

For investigating vortex formation in rotating superfluid ³He-B at high velocities of vortex-free superflow, the usual geometry is a cylindrical sample, which is connected via an orifice and a liquid ³He column to the heat exchanger on the refrigerator. The orifice prevents vortices, created in the heat exchanger, from flowing into the sample until the rotation velocity reaches a critical value Ω _c. We describe NMR measurements of Ω _c as a function of temperature and discuss the results in terms of vortex-line pinning at the rim of the orifice.