Investigation of aging in the HERA-B Outer Tracker drift tubes

The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar CF/sub 4/ CO/sub 2/ as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects-like Malter currents, gain loss due to anode aging and etching of the anode gold surface-have been observed and cures by tuning of operation parameters have been developed.