Etude des échanges thermiques et conception d’un système de refroidissement pour le système de lecture du trajectographe SciFi de LHCb

In the context of the evolution of the biggest circular accelerator of particles «LHC», an important program of upgrade on all the detectors which establishes itself was thrown. Among them, we find the upgrade of the detector LHCb which includes the complete replacement of several sub-detectors. The frequency of high reading of 40MHz, an unprecedented in an experiment of physical appearance of particles, and the environment of severe radiation bound to the increase of the intensity of the LHC, are the main challenges by the new sub-detectors. The work presented in this manuscript, described as a small part of the evolution of the LHCb detector. The development and the construction of a new wide-scale tracker, based on a new technology with scintillating fiber «SciFi», read with photomultipliers to the silicon «SiPM», is one of the key projects of the LHCb upgrade program. The first part, consists in studying the thermal exchanges and designing a cooling system for every Read-Out Box «ROB» which contains two electronic front-end « FE », and which allow to read the data of the detector. The latter has a thermal dissipation about 110W. To ensure the smooth running of electronic components, it is compulsory to set up a cooler. Important constraints are taken into account in this study, the first one represents the space limited compared to the need for the cooling system, the electronic interfaces and mechanical, the second concerns the SiPM. Connected with the electronics by flexible cables, they are located near the electronics «FE» and their temperature of operation is perfectly settled around -40 ° C. Works of digital simulations on the software FloTHERM and ANSYS were led on the experimental bench realized within the laboratory, and which allowed us to determine the best adapted solution of cooling. This study also showed to us that he is more than necessity to integrate thermal interfaces «IT» such as thermal pastas to assure a better transfer of heat between electronic components and cooler. The second part, represents an in-depth study on the thermal interfaces which are a delicate point of transfer of heat, because they can have dozens percent of the global thermal resistance. To guarantee an adequate and sustainable use of these materials, several parameters were verified, in particular hardness, consistency (no production of fat or oil) and the thermal conductivity, thanks to a bench of measures adapted according to the method normalized ASTM D5470, with this bench we could measure the flow of heat through the tested thermal interface sample and which is generated by a hot source and a cold source that are mounted at the ends of our bench.With the installation CHARME (CERN) and PAVIRMA (Cézeaux), a series of measure of irradiations at the neutrons and the X-rays are also made, correspond-ing to the environment in which they will be exposed in the experience, on one side to identify the damages and the possible changes on the thermal resistances by the analysis of the thermal impedance, the other one to identify the thermal interface which suits best our application and which allows to assure an excellent thermal exchange and thus a good cooling of the frontal electronics within the trajectographe of the detector LHCb.Dans le cadre de l’évolution du plus grand accélérateur circulaire de particules « LHC », un important programme de mise à niveau sur l’ensemble des détecteurs qui le constitue a été lancé. Parmi eux, on retrouve la mise à niveau du détecteur LHCb qui comprend le remplacement complet de plusieurs sous-détecteurs. La fréquence de lecture élevée de 40MHz, sans précédent dans une expérience de physique des particules, et l’environnement de rayonnement sévère lié à l’augmentation de l’intensité du LHC, sont les principaux défis à relever par les nouveaux sous-détecteurs. Le travail présenté dans ce manuscrit, décrit une petite partie de l’évolution du détecteur LHCb. Le développement et la construction d’un nouveau trajectographe à grande échelle, basé sur une nouvelle technologie à fibres scintillantes «SciFi», lues avec des photomultiplicateurs au silicium «SiPM», est l’un des projets clés du programme de mise à niveau de LHCb. La première partie, consiste à étudier les échanges thermiques et à concevoir un système de refroidissement pour chaque Read-Out Box « ROB » qui contient deux cartes électroniques frontales « FE », et qui permettent de lire les données du détecteur. Ces dernières possèdent une dissipation thermique d’environ 110W.Pour assurer le bon fonctionnement des composants électroniques, il est obligatoire de mettre en place un refroidisseur. Des contraintes importantes sont prisent en compte dans cette étude, la première représente l’espace limité en regard du besoin du système de refroidissement, des interfaces électroniques et mécanique, la seconde concerne les SiPM. Reliés à l’électronique par des câbles flexibles, elles sont situées à proximité de l’électronique « FE » et leur température de fonctionnement doit être parfaitement réglée autour des -40°C. Des travaux de simulations numériques sur les logiciels FloTHERM et ANSYS ont été menés sur le banc expérimental réalisé au sein du laboratoire, et qui nous ont permis de déterminer la solution de refroidissement la mieux adaptée. Cette étude nous a aussi montré qu’il est plus que nécessaire d’intégrer des interfaces thermiques « IT» telles que des pâtes thermiques afin d’assurer un meilleur transfert de chaleur entre les composants électroniques et le refroidisseur. La deuxième partie, représente une étude approfondie sur les interfaces thermiques qui sont un point délicat de transfert de chaleur, car elles peuvent avoir plusieurs dizaines de pour cent de la résistance thermique globale. Pour garantir une utilisation adéquate et durable de ces matériaux, plusieurs paramètres ont été vérifiés, en particulier la dureté, la consistance (pas de production de graisse ou d’huile) et la conductivité thermique, grâce à un banc de mesures adapté d’après la méthode normalisé ASTM D5470, grâce auquel on a pu mesurer le flux de chaleur qui traverse l’échantillon d’interface thermique testé et qui est généré par une source chaude et un source froide qui sont montées aux extrémités de notre banc.Grâce à l’installation CHARME (CERN) et à la plate-forme PAVIRMA (Campus des Cézeaux), une série de mesure d’irradiations aux neutrons et aux rayons X sont également effectuées, correspondant à l’environnement dans lequel elles seront exposées dans l’expérience, d’un côté pour identifier les dégradations et changements possibles sur les résistances thermiques par l’analyse de l’impédance thermique, de l’autre pour identifier l’interface thermique qui convient le mieux à notre application et qui permet d’assurer un excellent échange thermique et donc un bon refroidissement de l’électronique frontale au sein du trajectographe du détecteur LHCb

Thermal study and design of a cooling system for the electronics boards of the LHCb SciFi tracker

The LHCb detector, one of the four large LHC detectors, has launched a major upgrade program with the goal to enormously boost the rate and selectivity of the data taking. The LHCb upgrade comprises the complete replacement of several sub-detectors, the substantial upgrade of the front-end electronics and the introduction of a new paradigm, namely the suppression of a hardware trigger by reading out the whole experiment synchronously at a rate of 40 MHz. The high readout frequency, unprecedented in a particle physics experiment, and the harsh radiation environment related to the increased LHC intensity, are the major challenges to be addressed by the new sub-detectors. The development and construction of a new large-scale tracking detector, based on a novel scintillating fibre (SciFi) technology, read out with silicon photomultipliers (SiPM), is one of the key projects of the LHCb upgrade program. The LHCb SciFi detector will count more than 500,000 channels. It is composed of 12 layers arranged in 3 tracking stations each with 4 planes of scintillating fiber modules and with a total sensitive area of about 340 m2. It is necessary to design an on-detector electronics allowing to readout the detector at 40MHz and to transmit the data at this frequency to the data acquisition system. The most challenging part for the FE electronics is the signal digitisation. A new front-end ASIC with 128 channels, the number of channels of a SiPM, is being developed to process and digitise the analogue signal from the SiPM. The hit position of the particle needs to be computed with a spatial resolution less than 100 μm. Four functions will be required to achieve this: amplification, shaping, integrating and digitisation. The boards hosting the ASIC and the clustering FPGAs, including the customised FPGA firmware are under design. Two front-end boards are used to read out half a SciFi module made of 2.5 m long fibre mats and are host in a Read Out Box (ROB). The power consumption of the boards in a ROB is around 120 W. In order to ensure the proper functioning of electronic components, it is mandatory to design a compact and efficient cooling system. It is worthwhile to notice that SiPM, which are connected to the electronics via flex cables, are located in the vicinity and their operating temperature must be regulated perfectly around -40° C. The first step to design the electronics cooling is to evaluate the energy balance of the electronic boards and to study the different cooling systems that may be appropriate. Once the modeling is done, the model is simulated with the FloTHERM and ANSYS softwares to find the more appropriate solution. The cooling system will be based on a demineralized water cooling system already existing in the LHCb cavern, but which will have to be redesigned to cope with the higher power consumption of the electronics, working at 19°C. Pipes going along the detector and through cooling blocks in Al or Cu will serve 5 or 6 ROB depending on the location. The electronic boards will be mounted on a radiator in Al which is screwed to two cooling blocks. The study of the cooling system has shown that it is more than necessary to integrate thermal interfaces such as thermal pastes in order to ensure a better thermal conductivity between the electronic components and the cooler. These interfaces are a delicate point of heat transfer because they can have several tens of percent of the overall thermal resistance. They therefore require a thorough knowledge of their behavior at thermal stresses, as well as their exposure to neutron and other radiation in which they will be surrounded during the operation of the experiment. In order to guarantee an adequate and durable use of these materials, several parameters have to be checked, in particular the hardness, the consistency (no grease or oil production) and the thermal conductivity. Thermal and radiation tests are therefore necessary in order to verify the resistance of the materials over the total duration considered for the detector, as well as hardness and thermal conductivity. Thermal conductivity measurement is an important and complicated part of the process. The appropriate method for measuring the thermal conductivity or thermal resistance of the interface material is based on ASTM D5470. A dedicated setup has been designed to perform these measurements. Prototypes of the different parts of the cooling system and of the electronics have been designed and built. Several tests have been conducted and the performances achieved will be presented

Study of thermal exchanges and design of a cooling system for the LHCb SciFi tracker reading system

Dans le cadre de l’évolution du plus grand accélérateur circulaire de particules « LHC », un important programme de mise à niveau sur l’ensemble des détecteurs qui le constitue a été lancé. Parmi eux, on retrouve la mise à niveau du détecteur LHCb qui comprend le remplacement complet de plusieurs sous-détecteurs. La fréquence de lecture élevée de 40MHz, sans précédent dans une expérience de physique des particules, et l’environnement de rayonnement sévère lié à l’augmentation de l’intensité du LHC, sont les principaux défis à relever par les nouveaux sous-détecteurs. Le travail présenté dans ce manuscrit, décrit une petite partie de l’évolution du détecteur LHCb. Le développement et la construction d’un nouveau trajectographe à grande échelle, basé sur une nouvelle technologie à fibres scintillantes «SciFi», lues avec des photomultiplicateurs au silicium «SiPM», est l’un des projets clés du programme de mise à niveau de LHCb. La première partie, consiste à étudier les échanges thermiques et à concevoir un système de refroidissement pour chaque Read-Out Box « ROB » qui contient deux cartes électroniques frontales « FE », et qui permettent de lire les données du détecteur. Ces dernières possèdent une dissipation thermique d’environ 110W.Pour assurer le bon fonctionnement des composants électroniques, il est obligatoire de mettre en place un refroidisseur. Des contraintes importantes sont prisent en compte dans cette étude, la première représente l’espace limité en regard du besoin du système de refroidissement, des interfaces électroniques et mécanique, la seconde concerne les SiPM. Reliés à l’électronique par des câbles flexibles, elles sont situées à proximité de l’électronique « FE » et leur température de fonctionnement doit être parfaitement réglée autour des -40°C. Des travaux de simulations numériques sur les logiciels FloTHERM et ANSYS ont été menés sur le banc expérimental réalisé au sein du laboratoire, et qui nous ont permis de déterminer la solution de refroidissement la mieux adaptée. Cette étude nous a aussi montré qu’il est plus que nécessaire d’intégrer des interfaces thermiques « IT» telles que des pâtes thermiques afin d’assurer un meilleur transfert de chaleur entre les composants électroniques et le refroidisseur. La deuxième partie, représente une étude approfondie sur les interfaces thermiques qui sont un point délicat de transfert de chaleur, car elles peuvent avoir plusieurs dizaines de pour cent de la résistance thermique globale. Pour garantir une utilisation adéquate et durable de ces matériaux, plusieurs paramètres ont été vérifiés, en particulier la dureté, la consistance (pas de production de graisse ou d’huile) et la conductivité thermique, grâce à un banc de mesures adapté d’après la méthode normalisé ASTM D5470, grâce auquel on a pu mesurer le flux de chaleur qui traverse l’échantillon d’interface thermique testé et qui est généré par une source chaude et un source froide qui sont montées aux extrémités de notre banc.Grâce à l’installation CHARME (CERN) et à la plate-forme PAVIRMA (Campus des Cézeaux), une série de mesure d’irradiations aux neutrons et aux rayons X sont également effectuées, correspondant à l’environnement dans lequel elles seront exposées dans l’expérience, d’un côté pour identifier les dégradations et changements possibles sur les résistances thermiques par l’analyse de l’impédance thermique, de l’autre pour identifier l’interface thermique qui convient le mieux à notre application et qui permet d’assurer un excellent échange thermique et donc un bon refroidissement de l’électronique frontale au sein du trajectographe du détecteur LHCb.In the context of the evolution of the biggest circular accelerator of particles «LHC», an important program of upgrade on all the detectors which establishes itself was thrown. Among them, we find the upgrade of the detector LHCb which includes the complete replacement of several sub-detectors. The frequency of high reading of 40MHz, an unprecedented in an experiment of physical appearance of particles, and the environment of severe radiation bound to the increase of the intensity of the LHC, are the main challenges by the new sub-detectors. The work presented in this manuscript, described as a small part of the evolution of the LHCb detector. The development and the construction of a new wide-scale tracker, based on a new technology with scintillating fiber «SciFi», read with photomultipliers to the silicon «SiPM», is one of the key projects of the LHCb upgrade program. The first part, consists in studying the thermal exchanges and designing a cooling system for every Read-Out Box «ROB» which contains two electronic front-end « FE », and which allow to read the data of the detector. The latter has a thermal dissipation about 110W. To ensure the smooth running of electronic components, it is compulsory to set up a cooler. Important constraints are taken into account in this study, the first one represents the space limited compared to the need for the cooling system, the electronic interfaces and mechanical, the second concerns the SiPM. Connected with the electronics by flexible cables, they are located near the electronics «FE» and their temperature of operation is perfectly settled around -40 ° C. Works of digital simulations on the software FloTHERM and ANSYS were led on the experimental bench realized within the laboratory, and which allowed us to determine the best adapted solution of cooling. This study also showed to us that he is more than necessity to integrate thermal interfaces «IT» such as thermal pastas to assure a better transfer of heat between electronic components and cooler. The second part, represents an in-depth study on the thermal interfaces which are a delicate point of transfer of heat, because they can have dozens percent of the global thermal resistance. To guarantee an adequate and sustainable use of these materials, several parameters were verified, in particular hardness, consistency (no production of fat or oil) and the thermal conductivity, thanks to a bench of measures adapted according to the method normalized ASTM D5470, with this bench we could measure the flow of heat through the tested thermal interface sample and which is generated by a hot source and a cold source that are mounted at the ends of our bench.With the installation CHARME (CERN) and PAVIRMA (Cézeaux), a series of measure of irradiations at the neutrons and the X-rays are also made, correspond-ing to the environment in which they will be exposed in the experience, on one side to identify the damages and the possible changes on the thermal resistances by the analysis of the thermal impedance, the other one to identify the thermal interface which suits best our application and which allows to assure an excellent thermal exchange and thus a good cooling of the frontal electronics within the trajectographe of the detector LHCb

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

The LHCb upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software