Radiation damage to doped Si Fibres in the LHC tunnel

Radiation induced attenuation in Germanium (Ge) doped and Ge majority Germanium-Phosphor (Ge-P) bi-doped optical fibres for the LHC tunnel is investigated. After a short description of the basic damage mechanisms, experimental data from a gamma irradiation test with a 60Co source is presented. It is shown that the formulations derived from standard kinetic models for defect generation can be used to describe the observed radiation induced attenuation. A prediction of the radiation induced attenuation in Ge-P and Ge doped fibres in the cleaning sections around IP7 during a nominal operational year of the LHC is given.