The evolution of vortices on the surface of normal He I

Abstract

Thermogravitational convection (Rayleigh—Bénard convection, RBC) occurs in a layer of normal He I heated from above, at temperatures below the liquid density maximum of 4He T ≤ Tm = 2.178 K. It is experimentally established that the appearance of RBC in the bulk of the layer is accompanied by the excitation of a vortex flow on the free surface of He I. With time, small vortices form two large-scale vortices (vortex dipole) in a cylindrical vessel, the dimensions of which are limited by the vessel’s diameter. As the temperature of the liquid rises above Tm, the convective motion in the bulk of the nonuniformly heated layer rapidly decays, but the vortex flow on the surface of He I is conserved. The results of studying the vortex system evolution in the absence of RBCs (without energy pumping) show that, during long-term observations (over 1300 s), the non-linear interaction between weakly damped large-scale vortices leads to the appearance of small vortices on the surface of He I.