As part of the luminosity increase of the Large Hadron Collider (LHC), the first phase of the ATLAS experiment upgrade is coming to an end, before a restart planned for early 2022. To meet the requirements of physics in a highly radiative environment with a high particle flux, the two internal wheels of the muon spectrometer will be replaced by new devices: the New Small Wheels (NSW).
After several years of R&D and production, IRFU has just sent the last of the 32 detection modules that will be integrated into the NSW at CERN. This corresponds to the assembly of about 400 m2 of gas detectors based on Micromegas technology: a record!
The ancients understood that heroes, like Orion with Sirius, need their faithful companion. IRFU engineers and physicists and their collaborators are no exception to the rule and have just completed the development of a modern Sirius, a key element of the super spectrometer separator (S3) under construction at GANIL. The tests having been successful and the system has been moved to GANIL for its final installation.
In Greek mythology, Sirius, Orion's faithful four-legged companion, an outstanding hunter, was transformed into a constellation and placed at his side. This famous canid also gave its name to the brightest star in the night sky. IRFU physicists have just honoured him in their own way, this time in the world of detectors.
The muon spectrometer of the ATLAS experiment has been an important contribution of IRFU since the design, and IRFU is still in charge of the alignment today. The spectrometer plays a key role in the reconstruction of high-energy muons, the detection of which is crucial for the search of phenomena beyond the Standard Model. The spectrometer consists of about 1200 muon chambers that form a gigantic edifice 44 m long and 24 m in diameter. Despite these imposing proportions, the relative positions of the chambers must be known with an accuracy of the order of 50 μm in order to achieve the optimum performance of the spectrometer. To this end, a network of optical lines is used to continuously monitor the positions of the chambers relative to each other, as well as their deformations. An elaborate procedure for reconstructing the 56,000 parameters determining the alignment (for the central part) has been developed by a team at IRFU in order to obtain the precision required for the reconstruction of high-energy muons. This method, adopted by the ATLAS collaboration, is presented for the first time in an ATLAS note.
The main objective of the KATRIN experiment is the measurement of the mass of the three neutrinos of the Standard Model of Particle Physics. But the analysis of the beta decay spectrum of tritium also allows to search for the trace of a hypothetical fourth neutrino, called sterile neutrino. The collaboration has just published its first analysis in Physical Review Letters (see article) based on four weeks of data acquired in 2019. There is no trace of this fourth neutrino, but this is only the beginning as sensitivity will rapidly improve. The KATRIN spectrometer shows a strong potential to study this possible new facet of the neutrino.
After more than four years of research and development, design and manufacturing work, the MFT (Muon Forward Tracker), a new detector that will equip the ALICE experiment at the LHC, has seen its construction finalized and is currently under commissioning at CERN. In order to limit as far as possible the amount of material crossed by the particles, the conception of this detector has required the development of many innovative techniques and procedures, particularly in the integration of silicon sensors on flexible hybrid circuits called ladders, for which Irfu was responsible within the project. It took two years to manufacture the 500 ladders of the MFT, and a very long sequence of operations was the subject of numerous studies under the responsibility of the Irfu Antenna team at CERN. The production of these ladders has just been successfully completed and it is therefore time to make a short assessment
As part of the new CLAS spectrometer project for the 12 GeV electron energy upgrade of the Jefferson Lab (USA) IRFU has been conducting R&D for more than 10 years to design and build a new generation tracker, using thin and flexible MICROMEGAS detectors that are now operating with the new CLAS12 spectrometer. After one year of installation, this tracker is operational and meets the expected characteristics with more than 95% detection efficiency and a spatial resolution of less than 100μm. After a dedicated data collection to measure the detector response, the new CLAS12 spectrometer is now collecting data for the DVCS physics experiment, where IRFU also participates and which objective is to measure the internal structure of the proton in three dimensions.
The exceptional success of the tracker project, that results from a close collaboration between IRFU's engineering and physics departments (DEDIP, DIS and DPHN), has been an example for other projects. Let us quote the LHC experiments for particle hunting, the muonic imaging of the pyramids, as well as a transfer of know-how to industry.
A prototype of the MXT camera arrived at the CNES in Toulouse on 25 October 2018. This is the Structural and Thermal Model (STM), which will be integrated into the telescope that will be sent to China to be mounted on the SVOM satellite Qualification Model.
The objective of this model is to validate the thermo-mechanical design of the camera. It also makes it possible to check the manufacturing and assembly capacity of the various components, which represent more than 1,000 elements. The model realized includes all the camera subassemblies with a good level of representativeness of the flight model, both on its external design (interfaces with the telescope) and on its internal design (harnesses, connectors...). The electrical parts (detector, electronic boards, motor) are replaced by weights and heaters to simulate their mechanical and thermal behaviour.
X-ray photons were detected for the first time in late August 2018 with an engineering model of the SVOM MXT focal plane. This is an important step towards the validation of the design of the detection chain.
The MXT telescope, for Microchannel X-ray Telescope, will be flown on board the SVOM satellite, a collaborative project between France (CNES) and China (CAS, CNSA) to study gamma-ray bursts. It aims at detecting soft X-rays (0.2 to 10 keV) at during the early phases of the afterglow emission, and at providing an accurate (smaller than 1 arc minute) position of the burst. Irfu is in charge of the design and realization of the telescope camera, integrating a pnCCD (provided by MPE) X-ray imaging spectrometer assembled on a dedicated ceramic board. The flight model of the detector must be integrated into the camera in one year from now.
The STEREO experiment presented its first physics results at the 53rd Rencontres de Moriond1. STEREO is a neutrino detector made up of six scintillation liquid cells that has been measuring, since November 2016, the electronic antineutrinos produced by the Grenoble high neutron flux reactor 10 metres from the reactor core. The existence of a fourth neutrino state, called sterile neutrino, could explain the deficit in neutrino flux detected at a short distance from nuclear reactors compared to the expected value. Indeed, this anomaly could result from a short-range oscillation that would result in less expected electronic antineutrinos being detected because they would disappear into sterile neutrinos. The first results obtained in 2018 after 66 days of data exclude a significant part of the parameter space. The experiment will continue to take data until the end of 2019. By multiplying the statistics by four and minimizing systematic analysis errors, STEREO will be able to shed light on the existence of this 4th neutrino family.
In the field of medical imaging, a IRFU team has launched a challenge: their goal is to image the brain activity with a precision of 1 mm3. Its name: CaLIPSO. The idea consists in an innovative detector technology: both light and ionisation signals produced by particle interactions are detected. For this, a series of technological obstacles must be overcome. One of these crucial steps has just succeeded. It consists in implementing the entire chain of ultra-purification of the detection liquid.
A team of physicists, engineers and technicians from IRFU are developing a new generation of MicroMegas trackers. The planned Compass II experiment at CERN, together with the Clas12 experiment at the Jefferson Lab, will impose new operational constraints preventing the current generation of trackers from working with nominal performance. Tests on a new generation of detectors have been carried out using particle beams generated at CERN. These tests have achieved both of their objectives; a reduction of the discharge rate which is a limiting factor in high flux experiments such as Compass, and a demonstration of their ability to operate under intense magnetic fields, a requirement for the gas detectors of the future Clas12 spectrometer. In a wider perspective, the development of MicroMegas technology is an essential component of the current IRFU research strategy with the recent establishment of a workshop dedicated to the design of this type of detectors.
Forest fires are a constant danger, particularly for arid countries. They act as a brake on economic development and are a threat to environment, by the large scale release of greenhouse gases as well as by the destruction of ecosystems.
The FORFIRE project, which includes the use of Micromegas1 detectors, has been supported by the European Union (FP7 program) in order to develop a network of sensors sensitive to the light emitted during a forest fire, allowing its almost instantaneous detection (opposed to the several minutes required by current methods).
The Micromesh Gaseous Structure (Micromegas) detectors designed and developed by IRFU researchers have been used increasingly over the past few years in the field of particle and radiation detection for physics research, and show strong potential for nuclear, biomedical and industrial instrumentation applications. Recent R&D efforts have led to the development of new manufacturing processes that improve the performance and scope of application of these detectors. The second generation of Micromegas detectors is already being used in several international physics experiments that have yielded excellent results since the fall of 2008.
A prototype of a novel charged particle detector has just been put to successful use by an IRFU-CERN-NIKHEF team working as part of the European EUDET project.
3D digital images of charged particle tracks have been obtained using the TimePix chip in conjunction with a Micromegas detector. This clears the way for building digital time projection chambers (TPCs) which could be used, for example, in building detectors for the future international linear collider (ILC). The novelty consisted in adding "clocks" to a more conventional chip to enable the arrival time of detection signals to be measured.
This large gas detector is based on a simple, strong and low-cost spherical geometry. The detector combines a large drift volume and proportional amplification in order to detect ionising particles. A metal ball at the centre of the sphere is held at a high voltage causing an avalanche effect in the gas surrounding it.
- Low energy neutrino physics
- industrial applications involving the detection of neutrons