Radiation-tolerant Multichannel Dew Point Temperature Monitoring System for High Energy Physics Applications

The next generation of high-energy physics (HEP) detectors will predominantly be silicon-based. As pixel sensor technology gains momentum and the number of channels surpasses one billion (for a volume of approximately 20 m3) to achieve the high resolution required for "imaging" charged tracks, current densities become very high, resulting in an overall power consumption of hundreds of kilowatts. Additionally, with increased collider luminosity, radiation levels rise, leading to higher sensor leakage current. Therefore, cooling becomes essential for removing the generated heat and preventing thermal runaway caused by temperature increases induced by the sensor leakage current. If not eliminated by cooling, this heat source creates a positive feedback loop with the increasing flow of leakage current due to its exponential temperature dependence.

Cooling the detectors and their environment has been a characteristic of Si HEP detectors since the 1990s. Due to the ever-increasing current requirements, powerful cooling systems capable of operating continuously for years, for cooling the detector components that operate in a high-radiation (1.2 Grad) and strong magnetic field (4 T ) environment, have become integral to the detector support structure. Cooling temperatures range between -40 and -25 â ŠC, and as the detectors cannot be permanently in an isolated environment, they are at risk of vapor condensation that may cause severe damage. To prevent damage from vapor condensation, reliable and detailed monitoring of the dew point temperature, and therefore humidity and ambient temperature, is necessary.

Temperature sensors that can survive in the detector environment, such as Resistance Temperature Detectors (RTDs), are commonly used. However, radiation-tolerant humidity sensors that provide the required resolution are not readily available. Therefore, the main objective of this dissertation was to select and characterize a suitable, affordable, and easy-to-integrate humidity sensor for the challenging HEP detector environment.

The chosen humidity sensor, the MK33-W, has demonstrated a linear dependence of its output on high accumulated proton fluence, which can be compensated for using a first-order polynomial function. Sensor responsivity has been tested at temperatures as low as -30â ŠC, where the sensor reliably provides information on the surrounding humidity level after calibration. Furthermore, the sensor has been exposed to a strong magnetic field, matching the one of the detectors, and has shown insensitivity to it.

Efficient, easy-to-deploy, and cost-effective multi-channel readout units for both humidity and temperature sensors have been proposed, considering the large number of sensors that will be distributed throughout the entire detector. Lastly, the integration of the developed systems into the CMS Detector Control System/Detector Safety System (DCS/DSS) has been discussed.