# Seminar on Condensed Matter Theory

Group of Theoretical Physics at the Department of Condensed Matter Physics

of Charles University has a pleasure to invite you to attend the seminar

on 11th May 2023 at 13:00

at Faculty of Mathematics and Physics of Charles University, Ke Karlovu 5, 121 16 Praha 2

Seminar room **F 052**

### Mgr. Emil Varga, Ph.D.

#### Department of Low Temperature Physics,

## Quasi-two-dimensional turbulent flows in superfluid helium

11. 05. 2023 13:00

# Mgr. Emil Varga, Ph.D. » Quasi-two-dimensional turbulent flows in superfluid helium

*Department of Low Temperature Physics, *

Mgr. Emil Varga, Ph.D.

Location: Seminar room KFKL, MFF UK (room F052 - ground floor near the rear staircase, Ke Karlovu 5)

Turbulent flows are chaotic and in three dimensions tend to destroy any order present in the flow. This behaviour changes drastically in two dimensions, where nonlinear processes lead to accumulation of energy at the largest scale through an inverse cascade, thus spontaneously ordering the flow into large-scale eddies. Superfluid helium is uniquely suited for the study of two-dimensional and quasi-two-dimensional turbulence, since the inviscid liquid easily flows into narrow channels and the interaction of quantized vorticity with thermal excitations (mutual friction) allows varying the dissipation suffered by the flow. Multiple types of critical phenomena in transition to turbulence are observed, with both flow velocity and temperature as control variables. The observed behaviour can be qualitatively explained through population dynamics of positive and negative discrete point vortices.