Problems and solutions in high-rate multi-channel hybrid photodiode design: the CMS experience

The unique conditions of the CMS experiment (4 Tesla magnetic field, restricted access, high neutron radiation, and 25 ns bunch-crossings) necessitated the development of a new type of high-rate multi-channel hybrid photodiode for the tile/fiber hadronic calorimeter. New complexities arose in the push toward high-rate operation, necessitating design changes in the diode structure and surface treatment. The product is now capable of high-rate operation with low crosstalk and leakage current. Lifetime studies of high voltage behavior, total charge, and irradiation have shown that the tubes will survive the 10 years of CMS running with only a few percent change in gain and manageable leakage current rise.