Chapter 1 Critical Velocities and Vortices in Superfluid Helium

Abstract

Publisher Summary This chapter focuses on the critical velocities and vortices in superfluid helium. The superfluid flow with vortex sheets becomes unstable at velocities higher than the critical one, and quantum vortex rings and lines are formed. In thin capillaries and in a film, this is connected with very great losses, because to create one vortex line, it is necessary to concentrate kinetic energy in a length of helium a hundred times larger than the film and capillary thickness. In large capillaries and with oscillating discs, the critical phenomena are connected not only with the appearance of the first vortex lines, but also with the kinetics of the development of quantum turbulence. The flow of the superfluid component relative to the walls, i.e. v s is responsible for the creation of the first vortex sheets and lines.. The counterflow of the superfluid and normal parts—that is v s -v u governs the kinetics of the development of quantum turbulence. For a more complete revelation of the nature of the critical velocities, it is necessary to get more precise values of the surface energy of vortex sheets in superfluid helium, as well as to clarify the kinetics of the transformation of vortex sheets into vortex lines and the further development of quantum turbulence.