Operation and performance tuning of ATLAS RPCs through the detector control system at the startup of 2009 LHC run

Detailed studies on the behavior of ATLAS Resistive Plate Chambers (RPCs) have been performed during the last year of ATLAS commissioning by using cosmic rays data and the first proton–proton collisions at 450 GeV. An overall status of the detector readiness and its performance at the start of Large Hadron Collider (LHC) operation is presented here. Detector parameters like the environmental variables (temperatures, pressures, gas mixture) or other working parameters (high voltage levels, front-end discriminating thresholds) are monitored and/or controlled by the Detector Control System (DCS). They have been used to optimize the efficiency and the stability of the system. Some examples of the correlations of these parameters with gas gap currents and trigger rates are presented here.