Czech Cryogenic Turbulence Facility

• First Laboratory in Europe utilizing particle imaging velocimetry and particle tracking visualization of cryogenic helium flow and superflow using micron size flakes of frozen hydrogen and/or hydrogen-deuterium mixture;
• Quantum turbulence studied in He II using second sound attenuation and small mechanical oscillators over entire ranges of pressure and temperature of superfluid 4He down to the zero temperature limit, including a new high cooling power commercial dilution refrigerator equipped with superconducting magnet up to 9 T;
• Ultra-high Rayleigh number (up to about 10¹⁵) turbulent convective flow using cryogenic helium gas as a working fluid.

Charles University in Prague, Faculty of Mathematics and Physics, recently invested into the abovementioned equipment for cryogenic fluid dynamics research, based on pre-existing cryogenic infrastructure. Following the devastating floods in Prague in 2002, a new cryohall (investment of 2500 k€) has been designed and built, opened in 2005, with helium liquefier (40 litres/hour, 920 k€) and skilled personnel capable of smooth supply of liquid helium for experiments at low and ultralow temperatures. During 2010 and 2011 the advanced cryogenic apparatuses (see below) extended the experimental horizon of the Department of Low Temperature Physics thus providing new options in cryogenic fluid dynamics research.

The CCTF 1 (liquid helium flow visualization) facility in Prague utilizes the well-known visualization methods of particle image velocimetry and particle tracking that have already proved highly useful in studies of conventional room temperature flows. This facility includes a 5W cw laser, fast (6.3 kHz) sensitive Phantom camera, all relevant optics as well as necessary hardware and software supplied by Dantec Dynamics. The helium flow occurs inside the optical tail (5 windows) of a custom-made low-loss open helium bath cryostat; temperatures down to about 1.1 K can be reached using an effective pumping unit based on a roots pump controlled via computer-operated butterfly-type valve. Tracer particles can be produced using a custom-built equipment from a gaseous hydrogen-deuterium-helium mixture; injecting it via a very fast computer-controlled valve into the helium bath. Flows of normal liquid helium as well as of its superfluid phase can be generated and studied.

The CCTF 2 (He II quatum turbulence) facility features a Leiden Cryogenics ³He – ⁴He dilution refrigerator equipped with a superconducting solenoid producing a vertical magnetic field up to 9 T. It was successfully tested on the supplier premises and is currently being installed in the cryohall in Prague. Two thin thermally anchored capillaries are available for filling and venting the custom-built experimental cells thermally attached to the mixing chamber. Various cells and flow generators, especially oscillating objects such as quartz tuning forks, vibrating wire resonators or grids will be used to address fundamental problems of quantum turbulence in the zero temperature limit in particular. At the appropriate temperature range, the mechanical oscillators may be supplemented by second sound attenuation sensors - a traditional detection technique in the Prague Laboratory – to measure the density of quantized vortex lines. Additionally, for experiments on quantum turbulence above 1.3 K a low-loss open bath cryostat equipped with a computer-controlled bellows flow generator is available.

The CCTF 2 (He II quatum turbulence) facility features a Leiden Cryogenics ³He – ⁴He dilution refrigerator equipped with a superconducting solenoid producing a vertical magnetic field up to 9 T. It was successfully tested on the supplier premises and is currently being installed in the cryohall in Prague. Two thin thermally anchored capillaries are available for filling and venting the custom-built experimental cells thermally attached to the mixing chamber. Various cells and flow generators, especially oscillating objects such as quartz tuning forks, vibrating wire resonators or grids will be used to address fundamental problems of quantum turbulence in the zero temperature limit in particular. At the appropriate temperature range, the mechanical oscillators may be supplemented by second sound attenuation sensors - a traditional detection technique in the Prague Laboratory – to measure the density of quantized vortex lines. Additionally, for experiments on quantum turbulence above 1.3 K a low-loss open bath cryostat equipped with a computer-controlled bellows flow generator is available.