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

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