1,721,071 research outputs found
The GEMpix detector as new soft X-rays diagnostic tool for laser produced plasmas
No full textLaser produced plasmas lend to several interesting applications. The study of X-ray emission from this kind of plasmas is important not only to characterize plasmas itself but also to study the application of these particular plasmas as intense X-ray sources. In particular several emission configurations can be obtained using different kinds of targets and tuning the characteristics of the laser pulse delivered to the target. Typically, laser pulse duration ranges between a few tens of femtoseconds and tens of nanoseconds, with energies from few mJ to tens of kJ. X-ray photon emissions last for times comparable to the laser pulses and during this time a great number of photons can be emitted. The following paper presents a measure of the soft-X-ray emission on the ECLIPSE laser facility realized with a new triple-GEM gas detector (GEMpix). It is a hybrid gas detector with a C-MOS front-end electronics based on Medipix chips. In the present work, different targets have been used in order to test X-rays of different energies. In this paper, in particular, we present results obtained for copper and iron targets. GEMpix is able to realize a 2D imaging of the X-ray emission from plasma with a signal proportional to the energy released in the gas of the detector active volume. Then through a preliminary single photon equalization realized at the NIXT lab (ENEA), also the number of photons reaching the area of the detector has been estimated. © 2016 Author(s)
GEM-based detectors for thermal and fast neutrons
No full textLately the problem of 3He replacement for neutron detection stimulated an intense activity research on alternative technologies based on alternative neutron converters. This paper presents briefly the results obtained with new GEM detectors optimized for fast and thermal neutrons. For thermal neutrons, we realized a side-on GEM detector based on a series of boron-coated alumina sheets placed perpendicularly to the incident neutron beam direction. This prototype has been tested at n@BTF photo-production neutron facilty in order to test its effectiveness under a very high flux gamma background. For fast neutrons, we developed new GEM detectors (called nGEM) for the CNESM diagnostic system of the SPIDER NBI prototype for ITER (RFX-Consortium, Italy) and as beam monitor for fast neutrons lines at spallation sources. The nGEM is a Triple GEM gaseous detector equipped with a polyethylene layer used to convert fast neutrons into recoil protons through the elastic scattering process. This paper describes the results obtained by testing a medium size (30 × 25 cm2 active area) nGEM detector at the ISIS spallation source on the VESUVIO beam line. © 2015, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg
Neutron diffraction measurements on a reference metallic sample with a high-efficiency GEM side-on 10B-based thermal neutron detector
No full textThe upgraded version of the GEM side-on thermal neutron detector was successfully tested in a neutron diffraction experiment on a reference sample using the INES diffractometer at the ISIS spallation neutron source, UK. The performance of the new 10B4C-based detector is compared to that of a standard 3He tube, operating at the instrument as a part of the detectors assembly. The results show that the upgraded detector has a better resolution and an efficiency of the same order of magnitude of a 3He-based detector. © 2018 EPLA
Tomographic 2-D X-ray imaging of toroidal fusion plasma using a tangential pinhole camera with gas electron multiplier detector
No full textA tangential X-ray pinhole camera based on a gas electron multiplier (GEM) detector was installed on KSTAR to study high temperature plasmas emitting X-ray photons in the energy band of 4–15 keV. The camera system consists of a triple-GEM gas chamber with a readout printed circuit board and a pinhole to image the plasma in two dimensions (2-D). The advantages of this tangential camera system include its compactness, high efficiency, energy discrimination in bands, and selectivity of the photon energy range etc. This camera system allows a selection of the viewing area through a remote control of the entire setup. The Philips-Tikhonov algorithm for tangential reconstruction was used to visualize the poloidal cross-sectional images. Phantom tests were performed with synthetic D-shaped plasma images and a comparison with the magnetic equilibrium flux surfaces from the real-time EFIT code obtaining a good agreement between each other. The 2-D X-ray images of the KSTAR plasma were successfully acquired during sawtooth crash, electron cyclotron heating, vertical displacement event, and emissivity from the injected trace Ar impurity. © 2016 Elsevier B.V
Major results from the first plasma campaign of the Wendelstein 7-X stellarator
No full textAfter completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 1019 m-3, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre. © 2017 Max-Planck-Institut fur Plasmaphysik
Timepix3 detector for measuring radon decay products
Full text linkThe present work is focused on the characterization of a
Timepix3 (TPX3) based test system for the identification of
particles produced by the complex decay chain of Rn. The
detector used is composed of a pixelated Cadmium Telluride (CdTe)
semiconductor (500 μm thick) bump-bonded on an ASIC TPX3
chip. Measurements were carried out at the NIXT Laboratory (ENEA
Frascati) using radioactive sources and exploiting the presence of
natural radon gas by collecting its decay products on the sensor
surface. Estimation of the radon gas risk is one of the most
important problems in radiation protection and has stimulated
further development of new advanced methods suitable for detecting
this gas in confined environments. A study of the spatial uniformity
and high energy calibration is also presented and an improved
cluster analysis is introduced. The performance highlighted in this
study will allow a detailed and faster analysis of the radon
products and may have an important impact on the environmental
radioprotection applications. This paper describes the application
and use of this test system to identify the different decay
signatures and follow the temporal evolution of the Radon decay
chain
A phenomenological model to study the energy discrimination potential of GEM detectors in the X-ray range
No full textAn empirical model is presented to study the operational characteristics of GEM detectors in the X-ray range and, in particular, its energy discrimination potential. Physical processes are modelled from a macroscopic point of view, to provide a simple but effective simulation tool. Experimental data from monochromatic and combined, two-line fluorescence sources, are used to validate the model and provide realistic estimates of the empirical parameters used in the description. The model is instrumental in understanding the role of threshold, gain and operational conditions to achieve energy-discriminating response. Appropriate choices of gas mixtures, threshold and gain will permit to best utilise this new functionality of the GEM to improve the efficiency of image detectors in applications ranging from in-situ imaging in harsh environments, such as tokamaks, to composite materials analysis and medical imaging of tissues. © 2015 Elsevier B.V
An hybrid detector GEM-ASIC for 2-D soft X-ray imaging for laser produced plasma and pulsed sources
No full textThe following paper presents a new 2-D detector ('GEMpix') in the soft X-ray range, having a wide dynamic range thanks to its intrisic gain, working in charge integration mode to be used for diagnosing laser produced plasma (LPP) or X-ray pulsed sources. It is a gas detector based on the Gas Electron Multiplier (GEM) technology with a quad-medipix chip as read-out electronics. In our prototype, the substitution of semiconductor material with a gas triple-GEM allows several advantages with respect to the detectors commonly used in LPP, as X-ray CCDs and Micro Channel Plates or Image Plates. In these experiments the configuration Time-over-Threshold (ToT) has been used, to measure the total charge released to the gas and collected by each pixel, integrated over the X-ray burst duration. Intensity response and spatial resolution has been measured first in laboratory for calibration, as function of the voltage applied to the GEMs, in single photon regime with energies between 3.7 and 17 keV. Subsequently it has been tested at the ABC laser facility (ENEA, Frascati). In this case, we measured the X-rays produced when the ABC neodymium laser, with pulse of 50 J and 3 ns time width, hits plane targets of aluminum. 2-D images have been acquired by means of a pinhole configuration with magnification 1.5 and 50 μm of spatial resolution. The results are encouraging regarding the capability of this imaging detector to work in experiments where soft X-ray emissivity varies over many orders of magnitude. © 2016 IOP Publishing Ltd and Sissa Medialab srl
Results and performances of X-ray imaging GEM cameras on FTU (1-D), KSTAR (2-D) and progresses of future experimental set up on W7-X and EAST Facilities
No full textThe triple Gas Electron Multiplier (GEM) is a good candidate for the observation of the plasma volume emitting X-rays photons in the energy band up to 30 keV. The GEM camera system can be simply installed outside the port of a fusion device and it's a micropattern proportional gas detector which consists of an ionization gap, where X-rays photon conversion occurs, three consecutive foils working as amplification stage and finally a dedicated printed circuit board. Its simple experimental setup can be made in different configurations with 1D or 2D imaging possibilities: perpendicular GEM camera allows a 1D emissivity profile reconstruction instead a tangential GEM camera allows a poloidal cross-section image. Moreover, they offer high sensitivity, noise free, optical flexibility (zooming and tilting, magnification 10× up to 30×), high contrast, high dynamic range (6 orders of magnitude) and good time resolution (submillisecond). In this work several experimental results already observed on the Frascati Tokamak Upgrade (FTU) and the Korean Superconducting Tokamak Advanced Research (KSTAR) devices will be presented. The perpendicular installation on FTU allows a 1D radial profile with 128 lines of sight, while thanks to the 2D tangential view of the plasma, the reconstruction of the cross section has been done on KSTAR. Between them there are dynamic and precursors of sawtooth, effects of Edge Localized Mode (ELM) in the core and possible interplay between core and edge in ELMs (high m modes), effects of plasma rotation in the core, dynamic of injected impurities in the outer part of the plasma or also impurity accumulation and localized effects of additional heating. Installation of GEM systems is planned on Wendelstein 7-X (W7-X) and the Experimental Advanced Superconducting Tokamak (EAST) also for their robustness and flexibility X-rays detection in presence of high radiative environments (neutrons and gammas). In future applications on the above mentioned fusion devices, another possibility under evaluation is to use standard tomographic methods using two orthogonal GEM camera systems. © 2017 IOP Publishing Ltd and Sissa Medialab
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