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Od odkrycia nadciekłości do kwantowej turbulencji

Magierski Piotr

Postępy Fizyki

2022

T. 73, z. 2

23--28

W 1927 roku Mieczysław Wolfke i Willem Keesom zaobserwowali przejście fazowe w ciekłym helu. Poniżej temperatury 2,28 K gwałtownej zmianie uległy własności cieczy nazwanej helem II. Nie wiedzieli, że właśnie odkryli nowy rodzaj substancji, której własności wynikają z efektów kwantowych ujawniających się w niskiej temperaturze. Ich zrozumienie było przez wiele lat wyzwaniem dla fizyków, a postępujące badania stworzyły nową gałąź fizyki: fizykę niskich temperatur.

In 1927 Mieczysław Wolfke and Willem Keesom have observed phase transition in liquid Helium. Below temperature of 2,28 K properties of the liquid, which dubbed Helium II, have changed abruptly. hey did not realize they had just discovered a new kind of substance, having properties which are consequence of quantum effects manifesting themselves at low temperatures. Their understanding remained a challenge for physicists for many years and progressing research has resulted in creation of a new branch of physics: low temperature physics.

On quantum turbulence in superfluid 4He

Lipniacki T.

Archives of Mechanics

2001

Vol. 53, nr 1

23-43

The alternative approach to the homogeneous quantum turbulence is proposed in order to derive the evolution equation for vortex line-length density. Special attention is paid to reconnections of vortex lines. According to our previous paper, the summary line-length change delta s of two vortex lines resulting from the reconnection (in the presence of counterflow Vns) can be approximated by the expression: .... The dynamics of vortex lines in the tangle is considered as a sequence of reconnections followed by "free" evolutions. For the steady-state turbulence, the average line-length change between reconnections has to be zero. If, for a given value of the counterflow, the line density is smaller than the equilibrium one, the reconnections occur less frequently and becomes positive. As a result, the line density grows until the equilibrium is restored. On the other hand, when the line-density is too large, the reconnections are very frequent, so the lines shorten between reconnections and the line density becomes smaller. The time derivative of total line density is proportional to the reconnection frequency multiplied by the average line-length change due to a single reconnection. The evolution equation obtained in the proposed approach resembles the alternative Vinen equation.