''Low temperature irradiation experiments of LHC thermometers''

This paper presents the advancement of a program being carried out in view of selecting the cryogenic temperature sensors to be used in the CERN LHC collider. About 10,000 sensors will be installed around the 26.6 km LHC ring, and most of them will be exposed to high radiation doses during the accelerator lifetime. During the four irradiation experiment of 1997, 180 thermometers from 6 types have been exposed to high neutron fluences (>1015 n/cl2) at the ISN (Grenoble, France) Cryogenic Irradiation Test Facility. A cryostat is placed in a shielded irradiation vault where a 20 MeV deuterons beam hits a thin Beryllium target, resulting in a well collimated and intense neutron beam. The characteristics of the cryogenic system, the acquisition and the irradiation facility are described. The main interest of this set-up is its ability to simulate the whole life of the LHC thermometers : same total neutron fluence, irradiation at superfluid Helium temperature, on-line acquisition of sensors resistance, several warm-up cycles. The resistance shifts of the different thermometer are presented. (author)