Liquid Nitrogen Cooling for Irradiation of Silicon Pixel Detectors for the CMS Experiment

Undergraduate Honors Thesis

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/gh93h100n

Abstract

The upgrades to the High Luminosity Large Hadron Collider (HL-LHC) impose unique challenges on inner tracker pixel sensors for the Compact Muon Solenoid (CMS) experiment, necessitating changes outlined as the Phase-2 upgrade. A metric that will be crucial to the success of these sensors is their radiation hardness over a 10 year lifetime. In January 2023, the CMS RD53B readout chips (C-ROCs) were irradiated up to 100 MRad at Sandia National Laboratories over three days. In order to best simulate the real working conditions at the CMS experiment, keeping the chips at a cool, steady temperature is key. A liquid nitrogen cooling system was implemented to keep the temperature of the sensors and ROCs stable at -20 °C. This system maintained temperature sufficiently for much of the irradiation, but some larger than expected fluctuations occurred due to electromagnetic interference (EMI) and liquid nitrogen transfer. Several of the wire bonds connecting RD53B chips to readout electronics were destroyed during the irradiation, leading to an inconclusive result with multiple speculated causes. Follow-up tests at CU Boulder were performed to examine several causes of failure and improvements to the liquid nitrogen cooling system were made in anticipation of a return to Sandia National Laboratories.

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