Electromagnetic Compatibility of a Low Voltage Power Supply for the ATLAS Tile Calorimeter Front-End Electronics

Abstract

The front-end electronics of the ATLAS Tile Calorimeter is powered by DC/DC converters that sit close to it. The performance of the detector electronics is constrained by the conducted noise emissions of its power supply. A compatibility limit is defined for the system. The noise susceptibility of the front-end electronics is evaluated, and different solutions to reduce the front-end electronics noise are discussed and tested. I. POWER DISTRIBUTION SCHEME FOR THE TILE CALORIMETER The front-end electronics of the Tile Calorimeter [1] is organized in drawers that are inserted in detector modules. Each drawer is 3 meter long and contains the front-end analogue and digitizing electronics for 45 photomultiplier tubes [2] in the case of the barrel modules. It is powered by eight regulated low voltage lines, and it is rated to consume a maximum power of 300W. Because a drawer requires a tight voltage regulation on its power lines, the low voltage power supply was designed to fit in its vicinity, as an extension of it. The environmental constrains such as radiation and magnetic field tolerance were solved with the design of custom DC/DC converters that are remotely controlled by an ELMB [3]. The power supply is located in a closed volume known as finger. The power supply is water cooled. Figure 1: Finger low voltage power supply of the ATLAS Tile Calorimeter. The finger low voltage power supplies (figure 1) are fed by bulk power supplies (200VDC) located in a control room. Auxiliary power supplies in the same control room are also required to power separately the monitoring and control circuitry. The power system (figure 2) is controlled by the Detector Control System (DCS) through a CANBus line that communicates with the ELMB of the power supply. The low voltage outputs are isolated from earth, but all the return lines are put in common inside the drawer. Figure 2: Tile Calorimeter power distribution scheme. NOISE PERFORMANCE TEST METHODS The front-end noise is composed by the drawer electronics noise, by the power supply noise and by the external couplings on the interconnecting cables (not studied here). A. System Noise. The achievable performance of the drawer electronics in terms of noise is limited by design. The system noise in each front-end channel was measured in detail on drawers that were powered with low noise linear power supplies. The system noise is evaluated in terms of high frequency and low frequency contributions from the data taken with the full data acquisition chain. The high frequency noise seen by the fast readout electronics is estimated from the pedestals data. The estimation is based on a selection of parameters computed over several runs and on all the channels of a drawer: • RMS of the pedestals distribution. • Gaussian property of the pedestals distribution. Module DRAWER LVPS Finger 200VDC