One-dimensional textures and critical velocity in superfluid 3He-A

We study theoretically the stability of flow in superfluid He-3-A. The calculations are done using a one-dimensional model where the order parameter defends only on the coordinate in the direction of the superfluid velocity v(s). We concentrate on the case that the external magnetic field II is perpendicular to v(s), where only a few results are available analytically. We calculate the critical velocity nu (c) at which the superflow becomes unstable against the formation of continuous vortices. The detailed dependence of nu (c) on the temperature and on the form of the underlying orbital texture (1) over cap (r) is investigated. Both uniform and helical textures of 1 and two types of domain-wall structures are studied. The results are partially in agreement with experiments made in a rotating cylinder.