Fast Timing for High-Rate Environments with Micromegas

The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate a Micromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkov-radiator front window, which produces sufficient UV photons to convert the ~100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ~50 primary photoelectrons, using a bulk Micromegas readout.Comment: MPGD2015 (4th Conference on Micro-Pattern Gaseous Detectors, Trieste, Italy, 12 - 15 October, 2015). 5 pages, 8 figure

Scale Dependence of Mean Transverse Momentum Fluctuations at Top SPS Energy measured by the CERES experiment and studies of gas properties for the ALICE experiment

The principal aim of the study of ultrarelativistic nucleus-nucleus collisions is the search for evidence of a transient state of deconfined quarks and gluons in the early, dense and hot stage of the reaction. Non-statistical event-by-event fluctuations of mean transverse momentum,p_T, have been proposed as a possible signature for the QCD phase transition, in particular for the critical point. However, the magnitude of the measured fluctuations is not as large as anticipated. Since fluctuations were characterized so far by one single (integral) number, it was difficult to estimate the many possible contributions to them. Taking into account the high available statistics offered by the CERES experiment combined with the full azimuthal acceptance, a differential study of mean p_T fluctuations is performed, which provides the sensitivity to discriminate among various correlation sources. For the first time at SPS energy, the charge-dependent mean p_T fluctuations have been analyzed as a function of the angular pair separation, Delta(phi), and of the separation in pseudorapidity, Delta(eta). Thus, we are able to show that the overall fluctuations are dominated by the short range correlation peak at small opening angles (`near-side'), most probably originating from Bose-Einstein and Coulomb effects between pairs of particles emitted with similar velocities. Another important contribution is a broad maximum at Delta(phi) = 180 degrees (`away-side') originating from back-to-back (jet-like) correlations. Since the fluctuations related to the critical point should be present for all opening angles the best strategy is to focus on the fluctuations in the region of 30 < Delta(phi) <60 degrees, free of the influence of the two mentioned components, and where the elliptic flow cancels out. Concerning the observed away-side peak, we demonstrate that it comes from high-p_T correlations that cannot be attributed to the elliptic flow. The second part of the thesis is dedicated to studies of gas properties for the ALICE experiment at the CERN LHC. Drift velocity and gain measurements have been performed for a number of gas mixtures in order to assess the effect of nitrogen which is expected to accumulate in the gas volume over long periods of running. The ALICE Transition Radiation Detector (TRD) is designed to work with a gas of 85 % Xe and 15 % CO2. Some of the nine isotopes of Xe have very high neutron capture cross-section leading to multi-gamma deexcitation cascades which produce background for the physical signals. An exhaustive study of this issue based on Monte Carlo simulations is presented, demonstrating that the level of this background is low enough not to cause deterioration in the performance of the detector. In addition, the resulting radioactivity and dose rate of the active gas system of ALICE TRD activated by slow neutrons is investigated and appear to be low and safe

A New Beam Loss Monitor Concept Based on Fast Neutron Detection and Very Low Photon Sensitivity

International audienceSuperconductive accelerators may emit X-rays and Gammas mainly due to high electric fields applied on the superconductive cavity surfaces. Indeed, electron emissions will generate photons when electrons impinge on some material. Their energies depend on electron energies, which can be strongly increased by the cavity radio frequency power when it is phase-correlated with the electrons. Such photons present a real problem for Beam Loss Monitor (BLM) systems since no discrimination can be made between cavity contributions and beam loss contributions. Therefore, a new BLM is proposed which is based on gaseous Micromegas detectors, highly sensitive to fast neutrons, not to thermal ones and mostly insensitive to X-rays and Gammas. This detector uses Polyethylene for neutron moderation and the detection is achieved using a 10B or 10B4C converter film with a Micromegas gaseous amplification. Simulations show that detection efficiencies &gt; 8 % are achievable for neutrons with energies between 1 eV and 10 MeV

Large High-Efficiency Thermal Neutron Detectors Based on the Micromegas Technology

Due to the so-called He-3 shortage crisis, many detection techniques for thermal neutrons are currently based on alternative converters. There are several possible ways of increasing the detection efficiency for thermal neutrons using the solid neutron-to-charge converters B-10 or (B4C)-B-10. Here, we present an investigation of the Micromegas technology The micro-pattern gaseous detector Micromegas was developed in the past years at Saclay and is now used in a wide variety of neutron experiments due to its combination of high accuracy, high rate capability, excellent timing properties, and robustness. A large high-efficiency Micromegas-based neutron detector is proposed for thermal neutron detection, containing several layers of (B4C)-B-10 coatings that are mounted inside the gas volume. The principle and the fabrication of a single detector unit prototype with overall dimension of similar to 15 x 15 cm(2) and its possibility to modify the number of B-10 or (B4C)-B-10 neutron converter layers are described. We also report results from measurements that are verified by simulations, demonstrating that typically five (B4C)-B-10 layers of 1-2 mu m thickness would lead to a detection efficiency of 20% for thermal neutrons and a spatial resolution of sub-mm. The high potential of this novel technique is given by the design being easily adapted to large sizes by constructing a mosaic of several such detector units, resulting in a large area coverage and high detection efficiencies. An alternative way of achieving this is to use a multi-layered Micromegas that is equipped with two-side (B4C)-B-10-coated gas electron multiplier (GEM)-type meshes, resulting in a robust and large surface detector. Another innovative and very promising concept for cost-effective, high-efficiency, large-scale neutron detectors is by stacking (B4C)-B-10-coated microbulk Micromegas. A prototype was designed and built, and the tests so far look very encouraging.Funding Agencies|European Unions collaborative Seventh Framework Program for research, technological development, and demonstration under the NMI3-II Grant [283883]; European Union [654000]; EU H2020 Brightness Project [676548]</p

Fast Timing for High-Rate Environments with Micromegas

The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate aMicromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkovradiator front window, which produces sufficient UV photons to convert the ∼100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ∼50 primary photoelectrons, using a bulk Micromegas readout

Fast Timing for High-Rate Environments with Micromegas

The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate aMicromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkovradiator front window, which produces sufficient UV photons to convert the ∼100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ∼50 primary photoelectrons, using a bulk Micromegas readout

A Micromegas Based Neutron Detector for the ESS Beam Loss Monitoring

International audienceBeam loss monitors are of high importance in high-intensity hadron facilities where any energy loss can produce damage or/and activation of materials. A new type of neutron BLM have been developed for hadron accelerators aiming to cover the low energy part. In this region typical BLMs based on charged particle detection are not appropriate because the expected particle fields will be dominated by neutrons and photons. Moreover, the photon background due to the RF cavities can produce false beam loss signals. The BLM proposed is based on gaseous Micromegas detectors, designed to be sensitive to fast neutrons and insensitive to photons (X and gamma). In addition, the detectors will be insensitive to thermal neutrons, since part of them will not be directly correlated to beam loss location. The appropriate configuration of the Micromegas operating conditions will allow excellent timing, intrinsic photon background suppression and individual neutron counting, extending thus the dynamic range to very low particle fluxes. The concept of the detectors and the first results from tests in several facilities will be presented. Moreover, their use in the nBLM ESS system will be also discusse