Zadorozhko O. Collective modes and relaxation processes in superfluid helium in inhomogeneous condition

The thesis combines results of research of superfluid liquid properties under inhomogeneous conditions caused by extraneous bodies and thermal streams. The general picture of evolution of the fast and slow modes is built, for the first time, with changing aerogel porosity. It is shown that behavior can be adequately described by modified Bio theory of sound propagation for a three-component environment taking into account tortuosity of acoustic way. The values of the hydrodynamic and effective viscosity coefficient He II are first measured by the vibrating quartz tuning fork method in a wide temperature range. It is shown that in hydrodynamic range the viscosity temperature dependence is described by the kinetic theory of He II. The hierarchy of relaxation processes is analyzed and the contribution of each process to the viscosity coefficient is obtained. It is revealed that the convection instability of superfluid mixtures 3Не-4Не occurs only after dissociation on dilute and concentration phase. It is argued that the reason of instability are processes on a border between dilution phases.