Nuclear heating inside an MTR reactor needs to be known in order to design and to run irradiation experiments which have to fulfill target temperature constraints. To improve the nuclear heating ...knowledge, an innovative calorimetric system CALMOS has been studied, manufactured and tested for the 70MWth OSIRIS reactor operated by CEA. This device is based on a mobile calorimetric probe which can be inserted in any in-core experimental location and can be moved axially from the bottom of the core to 1000 mm above the core mid-plane. Obtained results and advantages brought by the first CALMOS-1 equipment have been already presented. However, some difficulties appeared with this first version. A thermal limitation in cells did not allow to monitor nuclear heating up to the 70 MW nominal power, and some significant discrepancies were observed at high heating rates between results deduced from the calibration and those obtained by the “zero method”. Taking this feedback into account, the new CALMOS-2 calorimeter has been designed both for extending the heating range up to 13W.g
-1
and for improving the “zero method” measurement thanks to the implementation of a 4-wires technique. In addition, the new calorimeter has been designed as a real operational measurement system, well suited to characterize and to follow the radiation field evolution throughout the reactor cycle. To meet this requirement, a programmable system associated with a specific software allows automatic complete cell mobility in the core, the data acquisition and the measurements processing. This paper presents the analysis of results collected during the 2015 comprehensive measurement campaign. The 4-wires technique was tested up to around a 4 W.g
-1
heating level and allowed to quantify discrepancies between “zero” and calibration methods. Thermal neutron flux and nuclear heating measurements from CALMOS-1 and CALMOS-2 are compared. Thermal neutron flux distributions, obtained with the Self-Power Neutron Detector suited to the CALMOS-2 calorimetric probe, are compared with those obtained with current devices. This campaign allowed to highlight advantages brought by the human machine interface automation, which deeply refined the profiles definition. Finally, the decay of the reactor residual power after shutdown could be performed after shutdown, demonstrating the ability of such type of calorimeter to follow the heating level whatever the thermohydraulic conditions, forced or natural convection regimes.
Ion backflow in the Micromegas TPC for the future linear collider COLAS, P; GIOMATARIS, I; LEPELTIER, V
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2004, Letnik:
535, Številka:
1-2
Journal Article
The International Linear Collider (ILC) Time Projection Chamber (TPC) transverse space-point resolution goal is
100
μ
m
for all tracks including stiff
90
∘
tracks with the full
∼
2
m
drift. A ...Micro-Pattern Gas Detector (MPGD) readout TPC can achieve the target resolution with existing techniques using 1
mm or narrower pads at the expense of increased detector cost and complexity. The new MPGD readout technique of charge dispersion can achieve good resolution without resorting to narrow pads. This has been demonstrated previously for
2
mm
×
6
mm
pads with GEMs and Micromegas in cosmic ray tests and in a KEK beam test in a 1
T magnet. We have recently tested a Micromegas-TPC using the charge dispersion readout concept in a high field super-conducting magnet at DESY. The measured Micromegas gain was found to be constant within 0.5% for magnetic fields up to 5
T. With the strong suppression of transverse diffusion at high magnetic fields, we measure a flat
50
μ
m
resolution at 5
T over the full 15
cm drift length of our prototype TPC.
Nuclear heating inside a MTR reactor has to be known in order to design and run irradiation experiments which have to fulfill target temperature constraints. This measurement is usually carried out ...by calorimetry. The innovative calorimetric system, CALMOS, has been studied and built in 2011 for the 70MWth OSIRIS reactor operated by CEA. Thanks to a new type of calorimetric probe, associated to a specific displacement system, it provides measurements along the fissile height and above the core. Calorimeter working modes, measurement procedures, main modeling and experimental results and expected advantages of this new technique have been already presented in previous papers. However, these first in-core measurements were not performed beyond 6 W · g -1 , due to an inside temperature limitation imposed by a safety authority requirement. In this paper, we present the first in-core simultaneous measurements of nuclear heating and conventional thermal neutron flux obtained by the CALMOS device at 70 MW nominal reactor power. For the first time, this experimental system was operated in nominal in-core conditions, with nominal neutron flux up to 2.7 10 14 n · cm -2 · s -1 and nuclear heating up to 12 W · g -1 . After a brief reminder of the calorimetric cell configuration and displacement system specificities, first nuclear heating distributions at nominal power are presented and discussed. In order to reinforce the heating evaluation, a comparison is made between results obtained by the probe calibration coefficient and the zero methods. Thermal neutron flux evaluation from SPND signal processing required a specific TRIPOLI-4 Monte Carlo calculation which has been performed with the precise CALMOS cell geometry. In addition, the Finite Element model for temperatures map prediction inside the calorimetric cell has been upgraded with recent experimental data obtained up to 12 W · g -1 . Finally, the experience feedback led us to improvement perspectives. A second device is currently under manufacturing and main technical options are presented.
We conducted a series of beam tests of prototype TPCs for the International Linear Collider (ILC) experiment, equipped with an MWPC, a MicroMEGAS, or GEMs as a readout device. The prototype operated ...successfully in a test beam at KEK under an axial magnetic field of up to 1
T. The analysis of data is now in progress and some of the preliminary results obtained with GEMs and MicroMEGAS are presented along with our interpretation. Also given is the extrapolation of the obtained spatial resolution to that of a large TPC expected as the central tracker of the ILC experiment.
Electron drift velocity measurements at high electric fields Colas, P; Delbart, A; Derré, J ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
02/2002, Letnik:
478, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
A method to measure the electron drift velocity is presented. A pulsed UV nitrogen laser is used to excite both the drift and cathode nickel micromeshes of a Micromegas detector. The signals induced ...on the anode are then readout by a fast current amplifier. Several results have been obtained for various gas mixtures and electric fields from
10
V/
cm
to
14
kV/
cm
. Relevant applications with low (TPCs mode) and high (pre-amplification mode) electric fields will be discussed.
Review on TPC's Lepeltier, Vincent
Journal of physics. Conference series,
04/2007, Letnik:
65, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Time-Projection Chamber invented thirty years ago by David Nygren, has been used very successfully for tracking in many particle and ion physics experiments, and is now often developed for rare ...events physics. After a presentation of the original idea of the TPC, and of the advantages of such a detector, the problems related to its realisation will be developed, then a panorama of TPCs for particle physics will be shown, and finally a survey will be done on potentialities of TPC for rare event detection.
Ion back-flow gating in a micromegas device Jeanneau, Fabien; Kebbiri, Mariam; Lepeltier, Vincent
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2010, Letnik:
623, Številka:
1
Journal Article
Recenzirano
As several research and development programs on Gaseous Photomultipliers are running on, the main aging factor on the photocathode, in particular for bi-alkali photocathodes, is the ion back-flow. ...This effect has also a major impact on the behaviour of Time Projecting Chamber in terms of electron drift perturbations. This paper presents a new device that has been tested with a Micromegas in order to reduce the ion back-flow in this type of detector. Instead of using a single mesh, as it is the case in a classical use of this micropattern detector, a double-mesh is installed. When the good conditions of electric field are applied, the device is transparent to electrons but gates the ions. Several measurements of ion back-flow ratio have been performed using a high power Xenon lamp to create photo-electrons on a Ni photocathode. The currents on the different electrodes are then measured with a pico-ammeter and the ion back-flow ratio is given by the ratio Ic/Ia (where Ic and Ia are respectively the cathode and the anode currents). For a classical mode of working (single mesh mode) the Micromegas ion back-flow is about few percent and is proportional to the field ratio. We have demonstrated that it is possible to reach a back-flow ratio close to few 10−6 in a double mesh mode, for a gain of several thousands, depending on the gas mixture and the electric fields ratio between the different electrodes.
Ion backflow in the Micromegas TPC for the future linear collider Colas, P.; Giomataris, I.; Lepeltier, V.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
2004, Letnik:
535, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
We present ion backflow measurements in a Micromegas (MICRO-MEsh GASeous detector) TPC device developed for the next high-energy electron–positron linear collider under study and a simple explanation ...for this backflow. A Micromegas micromesh has the intrinsic property to naturally stop a large fraction of the secondary positive ions created in the avalanche. It is shown that under some workable conditions on the pitch of the mesh and on the gas mixture, the ion feedback is equal to the field ratio (ratio of the drift electric field to the amplification field). Measurements with an intense X-ray source are in good agreement with calculations and simulations. The conclusion is that in the electric field conditions foreseen for the Micromegas TPC (drift and amplification fields, respectively, equal to 150–200
V/cm and 50–80
kV/cm) the expected ion backflow will be of the order of 2–3
×
10
-
3
. In addition, measurements have been done in a 2
T magnetic field: as expected the ion backflow is not altered by the magnetic field.
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