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

We study theoretically the stability of flow in superfluid He-3-A. The calc ulations are done using a one-dimensional model where the order parameter d efends 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 perp endicular to v(s), where only a few results are available analytically. We calculate the critical velocity nu (c) at which the superflow becomes unsta ble against the formation of continuous vortices. The detailed dependence o f nu (c) on the temperature and on the form of the underlying orbital textu re (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 parti ally in agreement with experiments made in a rotating cylinder.