New 80 K cryo-mechanical pump project

The 20 K cryo-mechanical pump (CMP) was built in Grenoble in 1996 and bench tested at Tore-Supra in 1998. Cold gas pumping concept, based on principle that gas density varies inversely with temperature, increases the mass flow rate treated by a given size pump when used at low temperature. Tests at several pumped gas temperatures (25 to 80 K) and pressures (10-1-10-4 Pa) were undertaken. The thermomolecular phenomenon in the pumping duct with thermal gradient was studied. Numerical and experimental data are presented and show that despite this effect, pumping system efficiency is increased when it is entirely cooled down. The CIEL project (toroidal pumped limiter) on 'Tore Supra' requires a maximum throughput of 6 Pa m3/s distributed on ten pumping ports. A new 80 K prototype study has been undertaken in collaboration with the vacuum industry to obtain a better cost efficiency on a ten standard CMP series. This prototype should be ready and tested on 'Tore Supra' at the end of 2001