Power Supply for the MDT detector of the ATLAS Experiment

Abstract

In this paper, the problem of the Low Voltage (LV) and High Voltage (HV) power supply distribution of the MDT (Monitored Drift Tubes) detector is addressed. Due to the high number of channels (1168 for low voltage and twice for high voltage) involved and to the dimension of the apparatus, these power supply systems are very complicated. These are composed mainly of three parts: a power generator, a system controller and an active distributor. The first two parts will be placed in the cavern close to the experimental area, so they are subjected to standard environmental conditions. The third part (the active distributor) will be placed in the experimental area on the platforms just outside the detector, in this case the environmental conditions are more severe, due to the presence of magnetic field (about 800 Gauss) and radiations. In the following we present the design specifications and tests for the power supply systems. I. THE ATLAS MUON SPECTROMETER In this section, the ATLAS Muon spectrometer layout, the MDT chamber description and the environmental condition in the experimental area, are briefly introduced. A. Muon Spectrometer Layout The ATLAS Muon spectrometer is composed of 1172 MDT chambers in total, (see, MDT layout Q rev. 13): 656 in the Barrel and 516 in the Endcap region (Figure 1). Figure 1: ATLAS muon spectrometer layout. It is subdivided into 16 sectors both in the Barrel part and in the Endcap, each sector covering an angle of 22.5 degree, (Figure 2). Moreover, this detector is divided in two symmetric sides with respect to the interaction point, the side A and side C. Figure 2: Muon spectrometer sectors. The MDT chambers [3] are composed of two multilayers separated by an aluminium frame called spacer, (Figure 3). Each multilayer is made, depending on the chamber type, of 3 or 4 layers of drift tubes each with 3 cm diameter, with lengths ranging from 1.5 to 6 meters. The drift gas is composed of Argon (93%) and CO2 (7%) and has been chosen mainly because of its favourable ageing properties in the LHC environment. The working pressure of the tubes is 3 bar absolute. Figure 3: Three layer barrel MDT chamber. B. ATLAS Muon Spectrometer Environment The ATLAS detector is installed in a cavern about 90 meters below the earth surface. This cavern is the experimental area and is called UX15, (Figure 4). The environmental conditions in this area are severe due to the presence of radiation and magnetic fields, whose values on the platforms just around the Barrel and Endcap, where the electronic racks will be installed, are reported in table 1. Table 1: UX15 environment parameters. Working temperature range 18 to 28 C Working humidity range 40 to 60 %RH Magnetic field 800 Gauss