Radiation Resistance and Life Time Estimates at Cryogenic Temperatures of Series produced By-pass Diodes for the LHC Magnet Protection

For the protection of the LHC superconducting magnets about 2100 specially developed by-pass diodes have been manufactured in industry and more than one thousand of these diodes have been mounted into stacks and tested in liquid helium. By-pass diode samples, taken from the series production, have been submitted to irradiation tests at cryogenic temperatures together with some prototype diodes up to an accumulated dose of about 2 kGy and neutron fluences up to about 3.0 1013 n cm-2 with and without intermediate warm up to 300 K. The device characteristics of the diodes under forward bias and reverse bias have been measured at 77 K and ambient versus dose and the results are presented. Using a thermo-electrical model and new estimates for the expected dose in the LHC, the expected lifetime of the by-pass diodes has been estimated for various positions in the LHC arcs. It turns out that for all of the by-pass diodes across the arc elements the radiation resistance is largely sufficient. In the dispersion suppresser regions of the LHC, on a few diodes annual annealing during the shut down of the LHC must be applied or those diodes may need to be replaced after some time.