Flow dissipation in the 3He superfluids

A review is given of the theoretical concepts relevant to experiments on the breakdown of superfluidity and flow dissipation in the 3He superfluids. In some sense, two phases seem to occupy extreme positions. The A (axial) phase, has been described as only accidentally superfluid, rescued from bulk instabilities in arbitrary small flows only by numerical coincidence. The superfluid current in the B (pseudo-isotropic) phase is limited by the kinetic energy of the flow competing with the condensation energy, leading to the ideal Landau-like critical velocity. 30 references, 1 figure