Speaker
Description
For the ATLAS Inner Tracker Pixel Outer Barrel, robust grounding and shielding (G&S) are critical to ensure the required detector performance. This contribution presents the G&S strategy developed to avoid ground loops, enhance common-mode noise rejection, and maintain shielding integrity for the pixel modules. Results from electromagnetic compatibility (EMC) testing of the first pre-production Loaded Local Support (LLS) are reported. Noise sensitivity to injected electric and magnetic fields and common-mode disturbances on power lines is quantified. Furthermore, G&S verification method and overall strategy for detector integration, including the use of the Ground Fault Monitor system, are discussed.
Summary (500 words)
In the high-luminosity era of the Large Hadron Collider, the instantaneous luminosity is expected to reach unprecedented values, resulting in about 200 proton-proton interactions in a typical bunch crossing. To cope with the resulting increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The innermost part of ITk will consist of a pixel detector, with an active area of about 14 m². The layout of the pixel detector is foreseen to have five layers of pixel silicon sensor modules in the central region and several ring-shaped layers in the forward regions. Among many novelties, the pixel modules will be powered serially in chains up to 14 modules to reduce the power consumption.
In this context, careful attention to grounding and shielding (G&S) is crucial to ensure the low-noise operation of the pixel detector, particularly the for the outer central layers of the detector: the Outer Barrel (OB) sub-system. A G&S strategy was defined early, focusing on the avoidance of ground loops, strict control of grounding paths, and the systematic use of common-mode noise rejection filters on all incoming and outgoing service lines. The entire OB is enclosed within a Faraday cage structure, with special consideration given to interfaces between modules, services, cooling and structural elements.
To validate the effectiveness of these design choices, electromagnetic compatibility (EMC) testing was performed on the first pre-production Loaded Local Support (LLS) – a major building block of the OB – fully equipped with pixel modules and associated services. External electric (E-field) and magnetic (B-field) noise was injected in a controlled manner, in various realistic scenarios, and the resulting impact on the noise at the level of the pixel modules’ analog channels was quantified. Additional tests involved the injection of common-mode (CM) currents into the power supply lines to study the system's resilience against conducted noise. These tests provided critical feedback on the effectiveness of the shielding measures, filtering strategies, and the sensitivity of various service paths.
Another major challenge addressed was the verification of grounding during the integration phase. Due to the complexity and scale of the OB system, standard continuity checks were insufficient. A strategy based on the use of the Ground Fault Monitor (GFM) was developed to detect unintentional ground connections and to monitor the integrity of the grounding scheme during integration and commissioning. To finalize the strategy, lumped-element equivalent circuit models were built and simulations were performed, taking into account constraints imposed by the integration tooling design and the practical feasibility of its production.
The contribution provides a comprehensive overview of the G&S strategy, its practical implementation, validation through EMC testing, and the ongoing efforts to maintain grounding integrity during large-scale system integration.
