The gain control system for the COPP (coincidence photon-proton) apparatus

We have built and operated a system which monitors and controls the response of the 12 lead-glass and the 12 plastic scintillator detectors in the COinfidence Photon-Proton (COPP) apparatus. We present here the detailed operation of the system and its performances during the experiment's runs. The gain control system, acting on the high-voltage values of the photomultiplier tubes, allows one to achieve a long term gain stability as good as 2% for each detector.