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Martinez-Fernandez J.,CIEMAT | Simonetto A.,CNR Institute for Plasma Physics Piero Caldirola | Cappa A.,CIEMAT | Soleto A.,CIEMAT
Fusion Engineering and Design | Year: 2017

This work describes the preliminary assessment of the different waveguide technologies for the ex-vessel transmission lines of the Plasma Position Reflectometer (PPR) in ITER. Using the available layout information at the initial stage of the PPR design, several waveguide dimensions of both rectangular waveguide and circular corrugated waveguides were evaluated; namely WR137, WR187, WR284, WR340 and WR430 in case of rectangular waveguides and 31.75. mm, 63.5. mm, 76.2. mm and 88.9. mm diameters for circular corrugated waveguides. In order to narrow the selection, an initial study was performed using available results from literature to obtain ohmic losses and mode conversion in mitre bends. Once the possibilities were trimmed, a final estimation was made using rigorous codes for the ohmic and mitre bend losses, also adding losses in waveguide gaps, on the selected candidates. This process led to the final estimation of performance for the preliminary routing of the PPR ex-vessel transmission lines. The chosen solution was 88.9. mm internal diameter circular corrugated waveguide, as the best compromise between in-band performance and space constraints. © 2017 Elsevier B.V.

Nemanic V.,Jozef Stefan Institute | Zajec B.,Jozef Stefan Institute | Dellasega D.,Polytechnic of Milan | Dellasega D.,CNR Institute for Plasma Physics Piero Caldirola | And 2 more authors.
Journal of Nuclear Materials | Year: 2012

We report results on long-term hydrogen outgassing and permeation studies of structurally highly disordered tungsten films, deposited on 40 mm diameter highly permeable Eurofer substrates, using the Pulsed Laser Deposition technique. Hydrogen interaction with tungsten is becoming a highly relevant topic since tungsten was recognized as the most promising candidate for the first wall of future fusion reactors. Prediction of hydrogen isotopes migration and their abundance after plasma exposure is uncertain due to a great role played by structural disorder that is formed on the W surface. Vacancy sites are theoretically predicted to trap multiple H atoms exothermically, but their density and their potential influence on permeability has not been experimentally investigated yet. In our work, permeability of W films having different thicknesses (1 and 10 μm) was initially extremely low, and was gradually increasing over a several-day campaign. The final values at 400 °C, lying between P = 1.46 × 10 -15 mol H 2/(m s Pa 0.5) and P = 4.8 × 10 -15 mol H 2/(m s Pa 0.5), were substantially lower than those known for well ordered films. Surprisingly, the 10 μm thick W film initially contained a very high amount of hydrogen, ∼0.1 H/W, which was gradually releasing during the twenty-day campaign. © 2012 Elsevier B.V. All rights reserved.

Alfonsi M.,CERN | Croci G.,CERN | Croci G.,CNR Institute for Plasma Physics Piero Caldirola | Duarte Pinto S.,CERN | And 5 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2012

The charging up effect is well-known in detectors containing dielectric materials and it is due to electrons and ions liberated in an avalanche and collected on the dielectric surfaces. In particular in Gas Electron Multiplier (GEM) based detectors, charges can be captured by the Kapton that separates top and bottom electrodes. The collection of a substantial number of charges on the dielectric surfaces induces a modification of the field inside the GEM holes that implies important consequences on some fundamental parameters such as the electron transparency and the effective gain. The correct simulation of this effect opens new ways to the detailed study of the processes that happens in a GEM-based detector and gives the possibility to optimise the GEM geometry in order to avoid it. This paper compares results of the measurements and the simulations, with and without the introduction of the charging-up effect, of the GEM electron transparency in the case of a single GEM detector. The introduction of the charging up effect in the simulation resulted to be crucial in order to get the proper agreement with the measurements. The measurements and simulations of the GEM effective gain will be the subject of a future work. © 2011 Elsevier B.V. All rights reserved.

Militello F.,EURATOM | Borgogno D.,Polytechnic University of Turin | Grasso D.,CNR Institute for Complex Systems | Marchetto C.,CNR Institute for Plasma Physics Piero Caldirola | Ottaviani M.,CEA Cadarache Center
Physics of Plasmas | Year: 2011

The linear stability of the tearing mode (TM) in a plasma column is investigated in the presence of viscosity and finite equilibrium current density gradients (i.e., asymmetries). It is shown that for low β, both effects are essential in order to properly describe the mode behaviour close to marginality. In particular, the theory introduces a critical threshold for the destabilization, such that the perturbation grows only if δ′ > δ′ cr. The value of δ′cr depends on the equilibrium configuration and on the plasma parameters. Most importantly, δ′cr can take negative values, thus allowing unstable tearing modes for δ′ < 0 (even in the absence of bootstrap current). © 2011 American Institute of Physics.

Rebai M.,University of Milan Bicocca | Rebai M.,CNR Institute for Plasma Physics Piero Caldirola | Milocco A.,University of Milan Bicocca | Giacomelli L.,University of Milan Bicocca | And 6 more authors.
Journal of Instrumentation | Year: 2013

Bi-parametric (neutron time of flight and deposited energy) measurements using a Single-crystal Diamond Detector (4.5 × 4.5 × 0.5 mm 3 active volume) were performed at the nTOF neutron facility at CERN. The time structure of the neutron beam combined with the long flight path allowed for measurements of the diamond detector response to quasi monoenergetic neutrons in the energy range up to 40 MeV. Deposited energy spectra were compared to MCNPX simulations using different cross section libraries. The results can be used for the interpretation of Single-crystal Diamond Detector measurements of fast neutrons at spallation neutron sources.© 2013 IOP Publishing Ltd and Sissa Medialab srl.

Del Sarto D.,CNRS Jean Lamour Institute | Marchetto C.,CNR Institute for Plasma Physics Piero Caldirola | Pegoraro F.,University of Pisa | Califano F.,University of Pisa
Plasma Physics and Controlled Fusion | Year: 2011

We provide numerical evidence of the role of finite Larmor radius effects in the nonlinear dynamics of magnetic field line reconnection in high-temperature, strong guide field plasmas in a slab configuration, in the large Δ′ regime. Both ion and electron temperature effects introduce internal energy variations related to mechanical compression terms in the energy balance, thus contributing to regularize the gradients of the ion density with respect to the cold regimes. For values of the Larmor radii that are not asymptotically small, the two temperature effects are no longer interchangeable, in contrast to what is expected from linear theory, and the differences are measurable in the numerical growth rates and in the nonlinear evolution of the density layers. We interpret such differences in terms of the change, due to ion temperature effects, of the Lagrangian advection of the 'plasma invariants' that are encountered in the cold-ion, warm-electron regime. The different roles of the ion and ion-sound Larmor radii in the reconnection dynamics near the X- and O-points are evidenced by means of a local quadratic expansion of the fields. © 2011 IOP Publishing Ltd.

Croci G.,CERN | Croci G.,CNR Institute for Plasma Physics Piero Caldirola | Alfonsi M.,CERN | Ropelewski L.,CERN | And 4 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

Neutron GEM-based detectors represent a new frontier of diagnostic devices in neutron-linked physics applications such as detectors for fusion experiments (Croci et al., 2012 [1]) and spallation sources (Murtas et al., 2012 [2]). Besides, detectors installed in HEP experiments (like LHC at CERN) are dip in a high flux neutron field. For example, the TOTEM T2 GEM telescope (Bagliesi et al., 2010 [3]) at LHC is currently installed very close to the beam pipe where a high intensity (>104ncm-2s-1) neutron background is present. In order to assess the capability (particularly related to discharge probability) of working in intense neutrons environment, a 10×10cm2 Triple GEM detector has been tested using a high flux (105ncm-2s-1) neutron beam. The neutron-induced discharge probability PDisch was measured to be 1.37×10 -7 at an effective gain G=5×104. In addition, the different types of neutron interactions within the detector were fully explained through a GEANT4 simulation. © 2013 Elsevier B.V.

Nocente M.,University of Milan Bicocca | Nocente M.,CNR Institute for Plasma Physics Piero Caldirola | Gorini G.,University of Milan Bicocca | Gorini G.,CNR Institute for Plasma Physics Piero Caldirola | And 3 more authors.
Nuclear Fusion | Year: 2011

The neutron emission from (3He)D plasmas with RF heating is calculated using a model that includes supra-thermal (knock-on) components of the deuteron population. The RF generation of fast 3He ions is described and the knock-on components were determined with the help of newly derived 3He + d scattering cross sections. Results are presented on the neutron emission spectrum and its contributions from different deuteron velocity components. It is shown that knock-on leaves an observable feature in the spectrum with a clear dependence on absorbed RF power. The importance of the nuclear interaction in the elastic cross section is demonstrated. The results represent a step forward in the use of neutron emission spectroscopy to diagnose fusion plasmas with minority supra-thermal components in their fuel ion composition. © 2011 IAEA, Vienna.

Chen Z.,Beijing University of Technology | Nocente M.,University of Milan Bicocca | Nocente M.,CNR Institute for Plasma Physics Piero Caldirola | Tardocchi M.,CNR Institute for Plasma Physics Piero Caldirola | And 3 more authors.
Nuclear Fusion | Year: 2013

The neutron emission spectrum from neutral beam-heated plasmas of the Experimental Advanced Superconducting Tokamak (EAST) is investigated based on first-principles simulations of the fast deuteron energy distribution. Parametrized plasma profiles are used to determine the beam deposition and fast deuteron distribution function using the NUBEAM code. The deuteron distribution is also interpreted with the help of empirical models and the components in the neutron energy spectrum are computed for different viewing lines using a Monte Carlo method. The resulting observational possibilities are discussed for the case of a time-of-flight neutron emission spectrometer optimized for EAST. © 2013 IAEA, Vienna.

Nocente M.,University of Milan Bicocca | Nocente M.,CNR Institute for Plasma Physics Piero Caldirola | Kallne J.,University of Milan Bicocca | Kallne J.,Uppsala University | And 4 more authors.
Nuclear Fusion | Year: 2013

The effects of nuclear elastic scattering (knock-on) from energetic light ions on the neutron emission spectrum in fusion plasmas are studied. The knock-on spectral features in D and DT plasmas without and with radio frequency heating on a 3He minority component are determined through Monte Carlo simulations. The neutron production magnitudes are determined relative to those due to fuel ions in the thermal bulk state (down to the level of 10 -5), and the interference of higher order terms in the outlying spectral regions where these dominate is evaluated. The study completes the mapping of nuclear reaction and elastic scattering effects on the neutron emission spectrum including first-, second- and third-order processes. Included are the cross-couplings between dd and dt fusion reactions as manifested in the full neutron spectrum (En = 0-20 MeV) for DT plasmas of varying isotopic composition. This study determines the relationship between components of the neutron emission spectra and those of the underlying ion velocity distributions, which provides a general basis for judging the plasma diagnostic information that can potentially be extracted from measurement and analysis of such neutron data. © 2013 IAEA, Vienna.

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