Extension of the operational lifetime of the proportional chambers in the HERMES spectrometer

The experience of the extension of the proportional chambers lifetime at the HERMES (DESY) experiment is presented. A non-invasive technique against the aging process while continuously operating the detectors in the gap of the HERMES spectrometer magnet was performed. It was found that adding 0.14% water to the 65%Ar+30%CO2+5%CF4 gas mixture perfectly cancelled the appearance of self-sustained current (Malter effect). The studies of the remedy for the lifetime extension were performed with the test prototypes of the original proportional chambers. For the complete recovery of the aged test proportional chambers a special training method was developed as well. Training of the aged proportional chamber at 80%CF4+20%CO2 mixture glow discharge with reversed high voltage demonstrated a complete recovery of the detector.