About the second sound pencils self-focusing in helium II

It is shown that with temperature T0≅1.9 K, where the linear dependence of second sound velocity on the counterflow velocity becomes zero, the coefficient of square dependence is positive. That contradicts the necessary condition of self-focusing - negative quantity of this coefficient. The monochromatic second sound wave of a large amplitude is distorted up to the gap formation in the fore fronts of positive and negative half-waves. The statement about the possibility of the second sound pencils self-focusing in helium II is shown to be conditioned by the substantial methodical mistake leading to incorrect equations of density continuity and superfluid motion. This mistake results in a negative coefficient of square dependence of the second sound velocity on the counterflow velocity. (author)