High voltage system

During data taking, the modules are operated typically with a total gap voltage of 8 kV. We chose to separately apply positive voltage to the anodes and negative voltage to the cathodes. This approach minimizes external discharges through and around insulators. Moreover, it helps reduce the overall HV system cost.
The LeCroy VISyN high voltage system is used which consists of Model 1458 mainframes and plug-in modules, Model 1468P for the anodes and Model 1469N for the cathodes. The cathodes are set at - 3.5 kV, and the anodes are set at + 4.7 kV for the barrel RPCs and + 4.5 kV for the end-cap RPCs. To reduce the system cost, the anode planes are ganged together and controlled by one positive high voltage channel. In the barrel, eight anode planes are ganged together, while in the end-caps, five anode planes are ganged together. The total current drawn by the RPCs during operation is approximately 5 mA or $\sim$ 1 $\mu$A/m$^2$ of the RPC area. For properly operating chambers, most of this current flows through the noryl spacers.