HARPO: a TPC as a gamma-ray telescope and polarimeter

A gas Time Projection Chamber can be used for gamma-ray astronomy with excellent angular-precision and sensitivity to faint sources, and for polarimetry, through the measurement of photon conversion to $e^+e^-$ pairs. We present the expected performance in simulations and the recent development of a demonstrator for tests in a polarized photon beam.Comment: SPIE Astronomical Telescopes + Instrumentation, Ultraviolet to gamma ray, Montr\'eal, Canada 2014. v2: note added in proof. Copyright 2014 SPIE. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibite

High-angular-precision gamma-ray astronomy and polarimetry

We are developing a concept of a "thin" detector as a high-angular-precision telescope and polarimeter for cosmic gamma-rays above the pair-creation threshold.Comment: Presented at the 6th International Conference On New Developments In Photodetection: NDIP 2011 4-8 Jul 2011, Lyon, Franc

Otimização adaptativa de um campo de poços vulnerável

International audienceThe contamination of groundwater resources is a challenge for drinking water supplies. To meet water quality standards, well-field operators need practical solutions to reduce the vulnerability of production wells. Strategies for several combinations ofmanagement variables such as well flow rate or water level in drains, are usually possible to satisfy the required production rate.However, these strategies may lead to contamination issues for the abstracted groundwater. A surrogate transport model wasimplemented in a well field vulnerable to a contaminated stream. An adaptive multi-objective optimization approach is proposed.The objective is to maximize the water production at the well field while minimizing the proportion of stream water abstracted.The optimization problem is adaptive to the stream level, which is a key parameter describing hydrological conditions. Asystematic exploration of management settings is conducted and a three-dimensional Pareto front is extracted. From theseoptimum settings, a practical easy-to-use approach is developed. The well-field operator can adjust production settings tooptimum conditions as a function of the observed stream water level and desired production rate.La contamination de la ressource en eaux souterraine est un défi pour l’approvisionnement en eau potable. Pour respecter les normes de qualité de l’eau potable, les exploitants ont besoin de solutions pratiques pour réduire la vulnérabilité des puits de production. La mise en place de stratégies jouant sur les schémas de gestion, telles que le débit des puits ou le niveau d’eau dans les drains, sont généralement possibles pour atteindre le débit de production requis. Cependant, ces stratégies peuvent entraîner des problèmes de contamination des eaux souterraines captées. Un modèle équivalent de transport a été mis en œuvre sur un champ captant vulnérable à un cours d’eau contaminé. Une approche d’optimisation multi-objectifs adaptative est proposée. L’objectif est de maximiser la production d’eau tout en minimisant la proportion d’eau du cours d’eau captée. Le problème d’optimisation est adaptatif au niveau du cours d’eau, paramètre clé décrivant les conditions hydrologiques. Une exploration systématique des paramètres de gestion est effectuée et un front de Pareto tridimensionnel est extrait. À partir de ces paramètres optimaux, une approche pratique et facile à utiliser est développée. L’opérateur peut ajuster les paramètres de production aux conditions optimales en fonction du niveau d’eau du cours d’eau observé et du débit de production souhaité

Quando a degradação de perclorato na bancada do rio não pode evitar a contaminação de poços de água potável

International audienc

Developing a particle tracking surrogate model to improve inversion of ground water – Surface water models

International audienceThe inverse problem of groundwater models is often ill-posed and model parameters are likely to be poorly constrained. Identifiability is improved if diverse data types are used for parameter estimation. However, some models, including detailed solute transport models, are further limited by prohibitive computation times. This often precludes the use of concentration data for parameter estimation, even if those data are available. In the case of surface water-groundwater (SW-GW) models, concentration data can provide SW-GW mixing ratios, which efficiently constrain the estimate of exchange flow, but are rarely used. We propose to reduce computational limits by simulating SW-GW exchange at a sink (well or drain) based on particle tracking under steady state flow conditions. Particle tracking is used to simulate advective transport. A comparison between the particle tracking surrogate model and an advective–dispersive model shows that dispersion can often be neglected when the mixing ratio is computed for a sink, allowing for use of the particle tracking surrogate model. The surrogate model was implemented to solve the inverse problem for a real SW-GW transport problem with heads and concentrations combined in a weighted hybrid objective function. The resulting inversion showed markedly reduced uncertainty in the transmissivity field compared to calibration on head data alone

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 > 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

GOLF-NG spectrometer, a space prototype for studying the deep solar dynamics

The GOLF-NG (Global Oscillations at Low Frequency New Generation) instrument is an instrument devoted to the space search of solar gravity and acoustic modes, and may be chromospheric modes. This instrument, successor of GOLF/SoHO will contribute to improve our knowledge of the dynamics of the solar radiative zone. It is a 15 points resonant scattering spectrometer, working on the D1 sodium line. The ground prototype is under construction to validate the hard points and will join the Teide Observatory, at Tenerife in 2006 to analyse how to separate the effects of magnetic turbulence on the line from the solar oscillations. We are prepared to put a space version of this instrument including a capability of identification of the modes, in orbit during the next decade. We hope to insert this search in the ILWS program. This instrument represents in combining observations with SDO and PICARD, a key to improve our knowledge of the solar core, in determining its rotation and magnetic field, through precise mode splitting measurements. The magnetic field of the radiative zone is fundamental for progressing on the solar activity sources, a clue for the long-term solar-earth relationship