P. Petagna

Microfluidic cooling for detectors and electronics

Micro-channel cooling is gaining considerable attention as an alternative technique for cooling of high energy physics detectors and front-end electronics. This technology is being evaluated for future tracking devices, where material budget limitations are a major concern. It is currently under investigation as an option for the cooling of the NA62 Gigatracker silicon pixel detector, where a micro-fabricated silicon cooling plate would stand directly in the beam. Other possible applications are also being studied in the context of LHC detectors upgrades. In this paper, the current status of this R&D at CERN is presented.

Nanoscale TiO 2 -coated LPGs as radiation-tolerant humidity sensors for high-energy physics applications

This Letter deals with a feasibility analysis for the development of radiation-tolerant fiber-optic humidity sensors based on long-period grating (LPG) technology to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN). In particular, here we propose a high-sensitivity LPG sensor coated with a finely tuned titanium dioxide (TiO₂) thin layer (~100 nm thick) through the solgel deposition method. Relative humidity (RH) monitoring in the range 0%-75% and at four different temperatures (in the range -10°C-25°C) was carried out to assess sensor performance in real operative conditions required in typical experiments running at CERN. Experimental results demonstrate the very high RH sensitivities of the proposed device (up to 1.4 nm/% RH in correspondence to very low humidity levels), which turned out to be from one to three orders of magnitude higher than those exhibited by fiber Bragg grating sensors coated with micrometer-thin polyimide overlays. The radiation tolerance capability of the TiO₂-coated LPG sensor is also investigated by comparing the sensing performance before and after its exposure to a 1 Mrad dose of γ-ionizing radiation. Overall, the results collected demonstrate the strong potential of the proposed technology with regard to its future exploitation in HEP applications as a robust and valid alternative to the commercial (polymer-based) hygrometers currently used.

Radiation hard polyimide-coated FBG optical sensors for relative humidity monitoring in the CMS experiment at CERN

This work investigates the performance and the radiation hardness capability of optical thermo-hygrometers based on Fibre Bragg Gratings (FBG) for humidity monitoring in the Compact Muon Solenoid (CMS), one of the four experiments running at CERN in Geneva. A thorough campaign of characterization was performed on 80 specially produced Polyimide-coated RH FBG sensors and 80 commercial temperature FBG sensors. Sensitivity, repeatability and accuracy were studied on the whole batch, putting in evidence the limits of the sensors, but also showing that they can be used in very dry conditions. In order to extract the humidity measurements from the sensor readings, commercial temperature FBG sensors were characterized in the range of interest. Irradiation campaigns with ionizing radiation (γ-rays from a Co60 source) at incremental absorbed doses (up to 210 kGy for the T sensors and up to 90 kGy for the RH sensors) were performed on sample of T and RH-Sensors. The results show that the sensitivity of the sensors is unchanged up to the level attained of the absorbed dose, while the natural wavelength peak of each sensor exhibits a radiation-induced shift (signal offset). The saturation properties of this shift are discussed.

STEADY-STATE HEAT TRANSFER THROUGH MICRO-CHANNELS IN PRESSURIZED HE II

The operation of the Large Hadron Collider superconducting magnets for current and high luminosity future applications relies on the cooling provided by helium-permeable cable insulations. These insulations take advantage of a He II micro-channels network constituting an extremely efficient path for heat extraction. In order to provide a fundamental understanding of the underlying thermal mechanisms, an experimental setup was built to investigate heat transport through single He II channels typical of the superconducting cable insulation network, where deviation from the macro-scale theory can appear. Micro-fabrication techniques were exploited to etch the channels down to a depth of ~ 16 im. The heat transport properties were measured in static pressurized He II and analyzed in terms of the laminar and turbulent He II laws, as well as in terms of the critical heat flux between the two regions.

Application of micro-channel cooling to the local thermal management of detectors electronics for particle physics

Micro-channel cooling is gaining considerable attention as an alternative technique for cooling of high energy physics detectors. This is of particular interest for future trackers, where large silicon surfaces are involved and the amount of material crossed by particles must be drastically reduced. Combining the versatility of standard micro-fabrication processes with the high thermal efficiency typical of micro-fluidics, it is possible to produce effective thermal management devices well adapted to different detector-specific applications. Three application cases are presented, which take into account different detector constraints and different refrigerant types: the first one being optimized for low temperature single-phase liquid flow, and the other two for evaporative cooling: one for low pressure/room temperature two-phase flow, and one for high pressure/low temperature two-phase flow.

The electro-mechanical integration of the NA62 GigaTracker time tagging pixel detector

The NA62 GigaTracker is a low mass time tagging hybrid pixel detector operating in a beam with a particle rate of 750 MHz. It consists of three stations with a sensor size of 60 x 27mm(2) containing 18000 pixels, each 300 x 300 mu m(2). The active area is connected to a matrix of 2 x 5 pixel ASICs, which time tag the arrival of the particles with a binning of 100 ps. The detector operates in vacuum at -20 to 0 degrees C and the material budget per station must be below 0.5% X-0. Due to the high radiation environment of 2 x 10(14) 1 MeV neutron equivalent cm(-2)/yr(-1) it is planned to exchange the detector modules regularly. The low material budget, cooling requirements and the request for easy module access has driven the electro-mechanical integration of the GigaTracker, which is presented in this paper.

Radiation hard humidity sensors for high energy physics applications using polymide-coated Fiber Bragg Gratings sensors

This work is devoted to a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics applications and in particular in the experiments actually running at the European Organization for Nuclear Research (CERN). On this line of argument, due to the wide investigations carried out in the last years aimed to assess the radiation hardness capability of fiber optic technology in high energy physics environments, our multidisciplinary research group has been recently engaged in the development and assessment of fiber optic sensors based on polyimide-coated Fiber Bragg Gratings (FBGs) to perform relative humidity (RH) monitoring at temperatures below 0°C as well as in presence of strong ionizing radiations. Data here reported, obtained during a deep experimental campaign carried out in the laboratories of CERN, demonstrate the amazing RH sensing properties of such sensors in the temperature range −15–20°C as well as their radiation hardness capability up to (at least) 10kGy dose of ionizing radiations.

Micro-channel cooling for high-energy physics particle detectors and electronics

Micro-channel cooling is gaining considerable attention as an alternative technique for cooling of High-Energy Physics (HEP) detectors and Front-End (FE) electronics. This technology is being evaluated for future tracking devices, where material budget limitations are a major concern. It has been approved as the baseline for the local thermal management of the NA62 GigaTracKer (GTK) silicon pixel detector, where a micro-fabricated silicon cooling plate would stand directly in the beam. Other possible applications are also being studied in the context of detectors upgrades for the CERN Large Hadron Collider (LHC). In this paper, the current status of this R&D at CERN is presented.

Evaporative CO 2 cooling system for the upgrade of the CMS pixel detector at CERN

Carbon dioxide (CO2) as evaporative coolant has gained interest as a technique for cooling of high-energy particle physics detectors and front-end electronics. Silicon tracking detectors need to be maintained at sub-zero temperature to enhance their lifetime in the presence of radiation damage. In addition, the material budget allocated to infrastructure must be as small as possible, to allow maximum transparency for tracking the trajectories of particles. Evaporative cooling is clearly the best method to meet these goals, and CO2 as coolant is an excellent option for this application as it can withstand a large amount of radiation and has excellent thermal behaviour in small diameter tubes. CO2 evaporative cooling has been selected for the next generation CMS Pixel detector, due in ~2016 to replace the present detector which is cooled with liquid C6F14. The design requirements for the new detector are an operating temperature of -10 °C on the silicon pixel sensor (-20 °C on the coolant) and a total power of about 15 kW. Following the successful applications in AMS and LHCb Velo projects, the 2-Phase Accumulator Controlled Loop method (2PACL) has been chosen and scaled up by a factor 10 in cooling power. Liquid CO2 is pumped from the cooling plant to the detector along 40-meter transfer lines. At the evaporators inside the detector, low vapour quality CO2 is fed at a constant pressure, with no need of active components in the vicinity of transfer lines the particle interaction region. This paper describes the general design of the Pixel system and the on-going tests of the detector on-board evaporators and long transfer line prototypes. This development is part of the CMS Pixel Upgrade project, and it is being carried out in the framework of the CMS Pixel Collaboration.

Review of results for the NA62 gigatracker read-out prototype

The Gigatracker (GTK) is a hybrid silicon pixel detector developed for NA62, an experiment studying ultra-rare kaon decays at the CERN SPS. The main characteristics are a time-tagging resoluion of 150ps, with low material budget per station (0.5% X0) and a fluence comparable to the one expected for the inner trackers of LHC detectors in 10 years of operation. To compensate the time-walk, two read-out architectures have been designed and produced. The first architecture is based on a Constant Fraction Discriminator (CFD) followed by an on-pixel Time-to-Digital-Converter (TDC). The second architecture is based on a on-pixel group shared TDC. The GTK system developments are described: the integration steps (assembly and cooling) and the results obtained from the prototypes fabricated for the two read-out architectures.