In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton ...irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·10
p∙cm
is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10
, responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10
in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.
The growing demand for miniaturized radiation-tolerant detection systems with fast responses and high-power budgets has increased the necessity for smart and efficient cooling solutions. Several ...groups have been successfully implementing silicon microfabrication to process superficial microchannels to circulate coolants, in particular, in high-energy physics experiments, where the combination of low material budget to reduce noise generated by multiple scattering events and high radiation fluences is required. In this study, we report tests performed on an 885-µm–thick vertically integrated system. The system consists of a layer of microfabricated silicon channels for temperature management integrated to radiation-tolerant microfabricated 3D sensors, with electrodes penetrating perpendicularly to the silicon bulk, bump-bonded to an ATLAS FE-I4 pixel readout chip of 100 µm thickness, 2 × 2 cm
2
, and 26,880 pixels (each measuring 250 × 50 μm
2
). The system’s electrical and temperature characterization under CO
2
cooling as well as the response to minimum ionizing particles from radioactive sources and particle beams before and after 2.8 ×10
15
n
eq
cm
−2
proton irradiation will be discussed.
The cooling systems of the future tracking detectors of the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN will be entirely based on CO2 refrigeration technology. The system is ...a booster refrigeration system, composed of a two stage primary part with transcritical R744 equipment and a low temperature secondary CO2 pumped loop. The primary refrigeration sub-system installed on surface provides cold R744 at −53∘C to the CO2 pumped loops installed 100 m underground and rejects the heat exchanged. The process must be reliable and remain stable regardless of the amount of heat exchanged, which will amount to hundreds of kilowatts and is expected to vary throughout the lifetime of the detectors. The paper discusses the concept adopted for the innovative transcritical R744 cycle and describes the technical details of the first prototype built.
In this work, we consider the estimation of temperature along the pipes of concentric heat exchanger tubes in which CO2 is the working fluid. The transport phenomenon is modeled using (2x2) linear ...hyperbolic partial differential equations, with one rightward equation for the hot flow and one leftward equation for the cold flow. Both flows exchange energy through the wall interface, which physically induces a coupling between the two dynamics. Our objective is to estimate the temperature distribution along the flows from measurements at the tubes boundaries only. In this framework, we propose an adaptive boundary observer that can estimate not only the full state of the system, but also unknown in-domain parameters. The design is based on transforming the error system via a finite-dimensional backstepping-like transformation into a desired filter-based system, for which standard backstepping observer techniques and adaptation laws can be used. The theoretical results are evaluated against the temperature measurements taken from a CO2 refrigeration apparatus built at CERN, Switzerland.
Future silicon detectors for High Energy Physics Experiments will require operation at lower temperatures to cope with radiation damage of the sensors and consequent increase of the dark current, ...beyond the limit of the current CO2 evaporative cooling system. This, together with many other requirements such as mass minimization and high radiation hardness, pushes the need of a new advanced cooling technology. The new coolant shall be able to approach ultra-low temperatures below −60 °C, withstand high radiation levels while having cooling lines diameters comparable to the currently achieved with the CO2 technology. Among different natural working fluids, krypton appears as a promising coolant for the thermal management of future detectors in high-irradiated environments. The thermodynamic properties of krypton do not allow the use of a pumped loop cycle but rather impose a need of a novel cooling technology. A new ejector-supported krypton cycle is presented, highlighting the cycle dynamics involved due to the different temperature levels normally encountered during the detector lifetime.
A test facility to investigate flow pattern transitions of vertical two-phase flow of CO2 has been built within the scope of the high-luminosity detector upgrades at the European Organization for ...Nuclear Research (CERN). Adiabatic flow pattern observations for both vertical up- and downflow are recorded with high-speed imaging in tubes of 8 mm inner diameter, with saturation temperatures in the range of −25°C to +5°C and mass velocities ranging from 100kgm−2s−1 to 450kgm−2s−1. A database of 431 flow pattern observations in upward and 123 in downward direction has been compiled. The recorded data have been analysed with machine learning techniques and a previously trained Frame- and Flow-Regime-Classifier is used for the flow regime classification. The observed two-phase flow pattern transitions did not match the transition lines of existing flow pattern maps. As a consequence, new transition lines for the bubbly-to-slug, slug-to-churn and churn-to-annular transitions have been developed for both vertical upflow and downflow respectively and condensed into new flow pattern maps. It is concluded, that the flow regime transitions are strongly depended on vapour quality, mass velocity, the flow direction and the fluid properties. Compared to horizontal flow, a dryout region is not observed and the liquid film of the annular flow regime dries out symmetrically at vapour qualities close to x=1.
•Flow pattern visualization of vertical two-phase flow of carbon dioxide (CO2).•Flow pattern observations recorded with a high-speed camera and high-speed imaging.•Flow patterns are analysed with computer vision and machine learning techniques.•Flow regime transitions determined with CNN based Frame and Flow Regime Classifier.•New flow regime transitions and flow pattern map for vertical two-phase flow of CO2.
Carbon dioxide (CO2) has emerged as a very suitable refrigerant for Tracker cooling applications in high-energy physics. It has been successfully implemented in a two-phase pumped-loop cycle on three ...experiments at CERN. CO2-based cooling systems will continue to be used for the next generation of Silicon detectors at CERN. These next generation detectors will be much larger and will be operated at much lower temperatures than those considered so far and thus the cooling systems will need to be correspondingly upgraded. The numerical simulation tool developed at CERN to inform such an upgrade is presented here, together with the results of its validation carried out using experimental data generated with a purpose-built test setup.
•Next-generation Silicon detectors will be larger and operate at lower temperatures.•Significant changes required in existing two-phase detector cooling system design.•Simulation tool developed to help design new system and its controls.•Tool used to model a prototype cooling plant and its control system.•Model validated against experimental data from the plant.
•Heat transfer measurements of flow boiling CO2 in 8 mm tubes in vertical upward direction.•A correlation to predict the dryout inception within the experimental domain is proposed.•Comparison of ...more than 1900 experimental data points to existing prediction models.•Heat transfer properties of CO2 are enhanced in vertical upflow compared to horizontal data.•A vertical multiplier is suggested to capture the trends with two existing prediction models.
Heat transfer measurements of flow boiling Carbon Dioxide (CO2) in vertical upward direction have been carried out with a dedicated test facility at the European Organization for Nuclear Research (CERN). The investigation covers saturation temperatures within a range of −25∘C≤Tsat≤+5∘C, mass velocities from 100kgm−2s−1≤G≤450kgm−2s−1 and heat fluxes of 5.3kWm−2 and 11.4kWm−2. The experiments have been conducted in a vertical upward evaporator of 8 mm inner diameter and 8 m length and a database of more than 1900 measurements has been compiled within the present study. The heat transfer mechanism is dominated by the nucleate boiling contribution and dryout is observed as a function of saturation temperature, mass velocity and heat flux. A correlation is proposed to predict the dryout inception within the experimental range where the onset of dryout has been observed. The results suggest that most commonly used heat transfer prediction models underpredict the heat transfer mechanisms of CO2. Moreover, the heat transfer coefficients of CO2 increase in vertical upward direction, compared to the data of horizontal studies. For that reason, a vertical multiplier is suggested to capture the trends of vertical upflow with two existing prediction models.
•Two-phase pressure drop of CO2 in horizontal, vertical upward and downward direction.•Influence of flow patterns on pressure oscillations.•Influence of mass velocity, vapour quality and fluid ...properties on pressure drop.•Comparison of experimental data to existing prediction models.•Data set of 1100 pressure drop measurements in horizontal and vertical directions.
Adiabatic pressure drop measurements of two-phase Carbon Dioxide (CO2) have been carried out in horizontal, vertical upward and downward direction with a dedicated test facility at the European Organization for Nuclear Research (CERN). A database of more than 1100 measurements, consisting of 512 data points in horizontal and 295 data points for each vertical up- and downflow respectively, has been compiled within this study. The experiments cover saturation temperatures from -25°C⩽Tsat⩽+5°C, mass velocities from 100kgm-2s-1⩽G⩽450kgm-2s-1 and are carried out in test sections with an inner diameter of 8 mm. The analysis of the pressure drop signals reveals that pressure fluctuations are increasing around the slug flow regime and the oscillation effects get magnified in vertical direction. The measurements in horizontal direction are compared to 18 frictional pressure drop models. For the comparison of the vertical data, 21 void fraction correlations accounting for the static head have been combined with the frictional models. The data sets of the horizontal and vertical upflow measurements are well predicted by several pressure drop models with an acceptable statistical significance. However, the prediction models perform less accurately for vertical downflow and it has been found that the static head is not well described by the void fraction correlations. In particular at low mass velocities, the effects of phase separation due to dominant buoyancy forces are not well incorporated by the void fraction models considered. In addition to the comparison of the entire data sets, subdivided analyses accounting for the flow patterns are provided within the present work.
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