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Volume 373 - The 28th International Workshop on Vertex Detectors (Vertex2019) - Large detectors
ATLAS Pixel Detector upgrade at High Luminosity LHC
J. Pater
Full text: Not available
In 2025 the Large Hadron Collider will be shut down to allow
upgrades to the accelerator and the experiments. After this
``Phase-II'' shutdown the LHC is expected to reach unprecedented
values of instantaneous luminosity, with hundreds of interactions in
each bunch crossing. This means much higher data rates and
occupancies and increased radiation damage for the
experiments. During the Phase-II shutdown the entire ATLAS Inner
Detector will be replaced by an all-silicon system called the Inner
Tracker (ITk). The innermost part of the ITk will be a
state-of-the-art pixel detector with about 13 m$^2$ of active
silicon, which will provide precision tracking capability up to
$\mid\eta\mid=4$. The outermost layers of the ITk pixel detector
are being designed to last the lifetime of the HL-LHC, collecting up
to 4000fb$^{-1}$ of Integrated Luminosity; the innermost two layers
will be replaced once, after about 2000fb$^{-1}$.\\
The ITk pixel detector will be instrumented with new sensors and
readout electronics to provide improved tracking performance and
radiation hardness compared to the current detector. The sensor type
will be dependent upon location in the detector: most of the
detector will be populated with thin planar silicon sensors, but
3D-silicon sensors will be used in the innermost layer, due to their
higher radiation tolerance and lower power consumption which eases
demands on the support structures. The sensors will be read out by
new ASICs, based on the one currently being developed by the RD53
Collaboration, which will be thinned to 150$\mu$m or less to save
Support structures will be made of carbon-based
materials, chosen for low mass, high stability and high thermal
conductivity. They will be cooled by evaporative carbon dioxide
flowing in thin-walled titanium pipes. Servicing the detector
reliably within the limited space available, and without introducing
excessive amounts of material, is a significant challenge. Data will
be transported electrically inside the detector, on cables carrying
1.28 Gb/s; conversion to optical signals will take place at larger
radii where the radiation background is less intense. Serial
powering has been chosen as the baseline for the system as it
minimises service cable mass.\\
The ITk pixel detector is currently in the final
stages of R\&D, with production scheduled to start in 2021.
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