No abstract available

[en] The tokamak TORE SUPRA built by the association EURATOM-CEA is routinely operated with a toroidal magnet made of Niobium Titanium cooled at 1.8 K by pressurized HeII. The paper will remind the reasons for such a choice and will describe the corresponding technical solutions. After several years of operation, the validity of the HeII cooling solution will be discussed on the basis of the actual and long term behaviour

No abstract available

[en] The special cryogenic requirements of TORE SUPRA have called for novel solutions. Pumping the 1,75 K (13 mb) helium bath is achieved by the use of a pair of centrifugal pumps operating at very low temperature, backed up by liquid rings pumps at room temperature. Four oil-lubricated screw compressors mounted in series-parallel form the main cycle helium compression set. The Joule-Thomson expansion valve is replaced by a mechanical expansion engine working with a bi-phase exhaust. The control of the refrigeration system is entirely automatic

[en] The paper reviews the understanding of superfluid helium with regard to its use as coolant for superconducting devices. The topics to be addressed include heat transfer properties of the stagnant fluid, cooling by forced flow superfluid helium, design principles for superfluid helium cryogenic systems and, finally, an illustration of these principles by a few practical examples. 18 refs

[en] We have developed closed cycle liquid helium refrigerators using a Joule Thomson circuit precooled by commercially available two staged Gifford Mac Mahon cryocoolers. The Joule Thomson counterflow heat exchangers are modular and have been thermo-hydraulically characterized. Fully automatic cool down and operation are achieved by two pneumatically driven by pass and expansion valves. Several apparatus have been built or are under assembly with cooling power ranging from 100 mW up to 5 Watt, for temperature ranging from 2.8 K up to 4.5 K. A trouble free operation with several warm up and cool down cycles has been proven over 7000 hours

[en] This new concept consists of a mechanical pump able to run at low temperature (25 K). Since gas density varies inversely with temperature, the pump could deliver much higher mass flow rate than at room temperature for a given size. Advantages of this concept are reduction of an order of magnitude in size and weight when compared to a conventional pump scaled to perform the same mass flow rate at room temperature. Results obtained at 80 K and 25 K with a Holweck type molecular drag pump of 100 mm diameter and with few stages of a turbomolecular pump running at the same temperatures, are given. This pump would be a solution to allow continuous tritium extraction and minimize the mass inventory for the ITER (International Tokamak Experiment Reactor). 5 figs., 2 tabs., 4 refs

[en] Pellet generators are needed to fuel long pulse tokamak plasmas. For this purpose, an experiment was carried out, using a new apparatus, in order to demonstrate the feasibility of a pellet generator functioning with magnetic refrigeration. This new cooling solution seems well adapted to continuous operation and the principle of a 1 Hz pellet generator is presented. (authors). 4 figs., 10 refs

[en] Heat exchangers in cryogenic refrigerators must meet conflicting requirements for high thermal efficiency and low frictional pressure drops. This is particularly true in helium II refrigerators where the gas stream leaves the cold source at 15 mbar. Perforated-plate heat exchangers are likely to offer better overall performances for that application than the widely used plate-fin heat exchangers. Through their design they combine a high thermal conductance in transverse direction with a low thermal conductance in axial direction. The present paper reports on the initial stage of development of a fabrication method using photochemical milling of copper plates and stainless steel spacers, and silver brazing for bonding. Comparison of preliminary test measurements and calculations in the 80 to 300 K temperature range with flow rates between 1 and 5 g/s has confirmed that predictable results can be obtained for the thermal efficiency and the pressure drop with an accuracy of a few percent. (authors). 8 refs., 3 figs

[en] The biomass is a local and renewable energy source, presenting many advantages. This paper proposes to examine the biomass potential in France, the energy valorization channels (thermochemical chains of thermolysis and gasification) with a special interest for the hydrogen production and the research programs oriented towards the agriculture and the forest. (A.L.B.)