- 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.
Facilities and equipment
CCTF1 (Liquid Helium Flow Visualization)
The CCTF 1 facility in Prague utilizes the well-known visualization methods of particle image velocimetry (PIV) and particle tracking velocimetry (PTV) 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 all 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 (Fig. 1). 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. Hydrogen/deuterium tracer particles (Fig. 2) can be injected via a very fast custom-built computer-controlled valve into the helium bath. Flows of normal liquid helium as well as its superfluid phase can be generated and studied.
CCTF2 (He II Quantum Turbulence)
The CCTF 2 facility features a Leiden Cryogenics 3He – 4He dilution refrigerator (Fig. 1 shows its low temperature inset) with a base temperature below 10 mK equipped with a 9 T superconducting solenoid. 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 can 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 (Fig. 2) is available.
CCTF3 (Helium Cryostat for Experimental Study of Natural Thermal Convection)
The CCTF 3 has been designed and constructed in collaboration with the Institute of Scientific Instruments, Academy of Sciences of the Czech Republic and is currently operated jointly in their premises in Brno. It currently contains a cylindrical (30 cm in diameter) aspect ratio one Rayleigh-Benard cell (low parasitic heat leak, smallest data corrections of generally acceptable form concerning sidewall and/or plates among all so far existing high Ra cryogenic cells) and will allow visitors to study the buoyancy driven flows up to Ra ~1015 under Boussinesq as well as non-Boussinesq conditions, utilizing the cryogenic helium gas (up to 3 bars) as a working fluid with well known and tuneable in situ physical properties. Small temperature sensors to measure temperature fluctuations and mean wind velocity are available. The cell geometry is easily customizable.