Paul Dervan

The data acquisition and calibration system for the ATLAS Semiconductor Tracker

The SemiConductor Tracker (SCT) data acquisition (DAQ) system will calibrate, configure, and control the approximately six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests

Thin silicon detectors for tracking in high radiation environments

The upgrade of the present Large Hadron Collider to high luminosity will impose the use of a factor of ten more radiation tolerant silicon sensors (microstrip and pixel) for the vertex and tracker system upgrades. The requirement for extreme radiation tolerance to hadron radiation is certainly the most stringent requirement for the HL-LHC sensors, but other parameters are also desirable, in particular a reduced mass of the whole systems. The use of thinner sensors than the standard 300 J.1m thick presently adopted could contribute to the reduction of the material in the acceptance volume of the experiments. It is now known that the thickness has also effects on the radiation tolerance of the sensors. The comparison of the signal generated by minimum ionising particles in 100, 140 and 300 J.1m thick sensors irradiated with reactor neutrons to various tluences up to the highest expected for the innermost pixel layers of the upgraded ATLAS experiment (2×1016 neq cm-2) are presented. Conclusions about the fluences where a given thickness gives the best signal are drawn from the experimental results to provide guidance for the optimal choice of thickness for segmented silicon sensors to be deployed in harsh hadron radiation environments.

The ATLAS SCT grounding and shielding concept and implementation

This paper describes the design and implementation of the grounding and shielding system for the ATLAS SemiConductor Tracker (SCT). The mitigation of electromagnetic interference and noise pickup through power lines is the critical design goal as they have the potential to jeopardize the electrical performance. We accomplish this by adhering to the ATLAS grounding rules, by avoiding ground loops and isolating the different subdetectors. Noise sources are identified and design rules to protect the SCT against them are described. A rigorous implementation of the design was crucial to achieve the required performance. This paper highlights the location, connection and assembly of the different components that affect the grounding and shielding system: cables, filters, cooling pipes, shielding enclosure, power supplies and others. Special care is taken with the electrical properties of materials and joints. The monitoring of the grounding system during the installation period is also discussed. Finally, after connecting more than four thousand SCT modules to all of their services, electrical, mechanical and thermal within the wider ATLAS experimental environment, dedicated tests show that noise pickup is minimised.