CERN - European Organization for Nuclear Research (EuTuCHe@CERN)
| Organisation: | CERN, European Organization for Nuclear Research |
|---|---|
| Location: | Geneva, Swizerland |
| Website: | http://public.web.cern.ch/public/Welcome.html |
| Contact: | Paolo Petagna |
Summary
- very High Reynolds ( up to 2x107) in axisymmetric jet and pipe geometries (HePipe, R+ up to 3x105)
- the whole range of flow scales, down to the Kolmogorov length (few microns) is accessible through movable, fast response, hot and cold wire anemometry in GReC
- Laboratory size experiments allowing modification and machining on their parts with standard laboratory equipment
- Flow properties well validated by previous experiments with various sensors (acoustic scattering, hot wire,...)
EuTuCHe@CERN takes advantage of the very low kinematic viscosity of gaseous and liquid He (600 times smaller than air), the most powerful liquid He pump available (1500 g/s) and dedicated kilowatts (cooling power at 4 K) cryogenic refrigerators to generate laboratory-size flows reaching very high Reynolds numbers. The flexibility offered by this approach allows exploring systematically the jet and pipe flows, which are paradigms of open and confined turbulent flows.
In the context of the EuHIT Trans-national Access programme, CERN will offer access to two distinct cryogenic installations, each one unique in Europe in terms of power and performance. Both installations depend on the Cryogenics group of the AT Department (Accelerator Technologies), but they are located in different buildings of CERNs Meyrin site (Geneva) and are independently operated by different technical teams: therefore it will be possible to provide access independently to both installations.
Operated in a stand-by duty service, the installations work without interruption throughout the year, except for the two weeks of end-of-year closure of CERN and three weeks of yearly maintenance for each installation. Their principal use is for the R&D, test and commissioning work on new cryogenic components for the LHC accelerator (like the 1800 superconducting magnets operating at 1.9K) or for High Energy Physics experiments (like the large superconducting magnets for the solenoid of the ATLAS experiment). The two installations are part of the unparalled CERN cryogenics inventory, which includes 8 refrigerators with 18 kW power at 4.5K, 6 refrigerators with 6 kW at 4.5 K and 14 others with power ranging from 0.1 to 1.5 kW at 4.5 K.
These characteristics make at present of CERN the absolute world-wide reference for large-scale cryogenics infrastructures, in terms of both installations and technical knowledge available on site. Many users from institutes collaborating to the LHC programme or to other HEP activities traditionally access the CERN cryogenic park every year. In the past few years, a group of researchers from different institutes in Grenoble proposed to CERN the use of one 6kW@4.2K refrigeration line for dedicated turbulent experiments: a special removable coaxial transfer line was designed, built and connected to a large cryostat used for the tests of LEP cavities, and the GReC installation (Grands Reynolds Cryogéniques) was born. Although the extremely reduced access time available till now, GReC successfully met the requirements of producing a controlled free jet with an integral Reynolds number ReD ranging from 7.7x105 to 1.01x107 (Rel from 1750 to 7100) in extremely stable conditions: <+/-5% in mass flow and =+/-1% in temperature and pressure. More recently, this success led to the request to adapt a second line, connected to a 1.2kW@4.5K refrigerator and a 1.5kg/s liquid helium pump, to produce a high Reynolds number confined flow: after modifications on the cryogenic line and the recent installation of a new 6.5m long, 36mm inner diameter pipe in the test section, the HePipe installation is now ready to operate, producing a controlled pipe flow with record values of ReD up to 2x107 and friction Reynolds Number Re+ up to 3x105.
The importance of cryogenic He flows for the study of turbulence in high Reynolds regimes, as an invaluable complement to the experimental studies conducted on conventional fluids, was strongly reaffirmed - if need there was- during the 3-days EuTuCHe international workshop held at CERN in April 2007 (LINK). More than 60 researchers from 10 countries gathered to discuss the achieved and potential results deriving from the use of cryogenic Helium for turbulence analysis, and their connections and synergies with the studies conducted in room temperature fluids. It was clear that the whole turbulence research community would largely benefit from widened access to state-of-the-art large-scale cryogenics installations. Notwithstanding the workload already charged on CERN cryogenics park, the beginning of the operational phase of LHC, partially alleviating the need for heavy test and commissioning activities, would provide a unique opportunity to offer direct and indirect access to the GReC and HePipe installations to a number of European researchers, up to now prevented from benefiting from the advantages of cryogenics flows due to the high costs and complex technologies involved. Fully conscious of the role that it can play in this direction, CERN has accepted to reserve a non negligible fraction of the yearly access to these two installations to groups of turbulence researchers in the context of a Trans-national Access programme.
Beside the direct scientific advances that will be brought by this new programme, it is also expected an important cultural impact on the participants. Not only through the dissemination of technical knowledge relevant to cryogenics and its use for science, but also, in a more general sense, through the direct contact with the scientific environment of HEP at CERN, a real melting pot of scientific, technical and cultural skills. The hands-on contact with the worlds largest international research centre, where scientists from different institutes and countries cooperate in a structured and integrated way to reach the required critical mass for fundamental science advances, each one still preserving his own autonomy and visibility, will certainly produce positive effects in terms of culture of structured scientific cooperation.