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Sökning: WFRF:(Tardocchi Marco)

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1.
  • Andersson Sundén, Erik, et al. (författare)
  • Evaluation of neutron spectrometer techniques for ITER using synthetic data
  • 2013
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 701, s. 62-71
  • Tidskriftsartikel (refereegranskat)abstract
    • A neutron spectrometer at ITER is expected to provide estimates of plasma parameters such as ion temperature, Ti, fuel ion ratio, nt/nd, and Qthermal/Qtot, with 10-20% precision at a time resolution, Δt, of at least 100 ms. The present paper describes a method for evaluating different neutron spectroscopy techniques based on their instrumental response functions and synthetic measurement data. We include five different neutron spectrometric techniques with realistic response functions, based on simulations and measurements where available. The techniques are magnetic proton recoil, thin-foil proton recoil, gamma discriminating organic scintillator, diamond and time-of-flight. The reference position and line of sight of a high resolution neutron spectrometer on ITER are used in the study. ITER plasma conditions are simulated for realistic operating scenarios. The ITER conditions evaluated are beam and radio frequency heated and thermal deuterium-tritium plasmas. Results are given for each technique in terms of the estimated time resolution at which the parameter determination can be made within the required precision (here 10% for Ti and the relative intensities of NB and RF emission components). It is shown that under the assumptions made, the thin-foil techniques out-perform the other spectroscopy techniques in practically all measurement situations. For thermal conditions, the range of achieved Δt in the determination of Ti varies in time scales from ms (for the magnetic and thin-foil proton recoil) to s (for gamma discriminating organic scintillator).
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3.
  • Gatu Johnson, Maria, 1978-, et al. (författare)
  • Neutron emission from beryllium reactions in JET deuterium plasmas with 3He minority
  • 2010
  • Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 50:4, s. 045005-
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent fast ion studies at JET involve ion cyclotron resonance frequency (ICRF) heating tuned to minority He-3 in cold deuterium plasmas, with beryllium evaporation in the vessel prior to the session. During the experiments, the high-resolution neutron spectrometer TOFOR was used to study the energy spectrum of emitted neutrons. Neutrons of energies up to 10MeV, not consistent with the neutron energy spectrum expected from d(d,n)He-3 reactions, were observed. In this paper, we interpret these neutrons as a first-time observation of a Be-9(He-3, n)C-11 neutron spectrum in a tokamak plasma, a conclusion based on a consistent analysis of experimental data and Monte Carlo simulations. Be-9(a, n)C-12 and Be-9(p, n)B-9 reactions are also simulated for p and a fusion products from d(He-3, a) p reactions; these two-step processes are seen to contribute on a level of about 10% of the single-step process in Be-9(He-3, n) C-11. Contributions to the total neutron yield from the Be-9(3He, n)C-11 reaction are found to be in the range 13 +/- 3 to 57 +/- 5%. We demonstrate how TOFOR can be used to simultaneously (i) probe the deuterium distribution, providing reliable measurements of the bulk deuterium temperature, here in the range 3.2 +/- 0.4 to 6.3 +/- 1.0 keV and (ii) provide an estimate of the beryllium concentration (in the range 0.48 +/- 0.17 to 6.4 +/- 1.7% of n(e) assuming T-3He = 300 keV). The observation of Be-9 related neutrons is relevant in view of the upcoming installation of a beryllium-coated ITER-like wall on JET and for ITER itself. An important implication is possible neutron-induced activation of the ITER vessel during the low-activation phase with ICRF heating tuned to minority He-3 in hydrogen plasmas.
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4.
  • Gatu Johnson, Maria, 1978-, et al. (författare)
  • Neutron emission levels during the ITER zero activation phase
  • 2010
  • Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 50:8, s. 084020-
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent experiments at JET, a contribution to the neutron emission from reactions between beryllium and 3He, 4He and H has been identified. With the beryllium walled planned for ITER, this raises the question of possible neutron activation during the ITER zero activation phase. Here, we estimate the neutron emission rates for various heating scenarios foreseen for this ITER phase using Monte Carlo simulations. The emission is seen to be strongly dependent on the scenario chosen and the assumptions involved. We find that fundamental minority heating can contribute on the scale of low temperature deuterium plasmas, depending on minority concentration and ICRH power applied. Harmonic ICRH leads to production of tails that can give rise to significant neutron emission rates, while rates from hydrogen beams will be near zero. Better knowledge of the zero activation phase conditions, and more sophisticated ICRH codes, would be needed to give exact rate predictions. We conclude that rates from so-called zero activation plasmas will be significantly lower than expected for the DD or DT phases, but far from zero.
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5.
  • Sjöstrand, Henrik, et al. (författare)
  • Fusion Power Measurement using a Combined Neutron Spectrometer-Camera System at JET
  • 2010
  • Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 57:2, s. 162-175
  • Tidskriftsartikel (refereegranskat)abstract
    • Fusion power production is the ultimate goal of fusion research, and its determination is crucial in any fusion energy application. In this paper the principles of collimated neutron flux measurements for fusion plasma power determination are described. In this method, a high-resolution neutron spectrometer provides an absolutely calibrated neutron flux, and a neutron profile monitor ("camera") gives information on the neutron emission profile of the plasma. The total neutron flux seen by the spectrometer is discussed in terms of direct and scattered flux, and a model is set up to evaluate the magnitude of these different components. Particular care is taken to estimate the uncertainties involved, both in the model and the measurements. The method is put to practical use at JET, where a magnetic proton recoil spectrometer and a neutron profile monitor are available. Results from JET's trace tritium experimental campaign in 2003 are presented and show that the systematic uncertainties in fusion power measurements are reduced in comparison to what has been presented for foil activation systems. A systematic error of 6% is reported here. For ITER these results imply that the fusion power can be redundantly measured and with better accuracies than for traditional methods.
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6.
  • Albani, Giorgia, et al. (författare)
  • Evolution in boron-based GEM detectors for diffraction measurements : From planar to 3D converters
  • 2016
  • Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 27:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The so-called '3He-crisis' has motivated the neutron detector community to undertake an intense R&D programme in order to develop technologies alternative to standard 3He tubes and suitable for neutron detection systems in future spallation sources such as the European spallation source (ESS). Boron-based GEM (gas electron multiplier) detectors are a promising '3He-free' technology for thermal neutron detection in neutron scattering experiments. In this paper the evolution of boron-based GEM detectors from planar to 3D converters with an application in diffraction measurements is presented. The use of 3D converters coupled with GEMs allows for an optimization of the detector performances. Three different detectors were used for diffraction measurements on the INES instrument at the ISIS spallation source. The performances of the GEM-detectors are compared with those of conventional 3He tubes installed on the INES instrument. The conceptual detector with the 3D converter used in this paper reached a count rate per unit area of about 25% relative to the currently installed 3He tube. Its timing resolution is similar and the signal-to-background ratio (S/B) is 2 times lower.
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7.
  • Biel, W., et al. (författare)
  • Diagnostics for plasma control - : From ITER to DEMO
  • 2019
  • Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 146:A, s. 465-472
  • Tidskriftsartikel (refereegranskat)abstract
    • The plasma diagnostic and control (D&C) system for a future tokamak demonstration fusion reactor (DEMO) will have to provide reliable operation near technical and physics limits, while its front-end components will be subject to strong adverse effects within the nuclear and high temperature plasma environment. The ongoing developments for the ITER D&C system represent an important starting point for progressing towards DEMO. Requirements for detailed exploration of physics are however pushing the ITER diagnostic design towards using sophisticated methods and aiming for large spatial coverage and high signal intensities, so that many front-end components have to be mounted in forward positions. In many cases this results in a rapid aging of diagnostic components, so that additional measures like protection shutters, plasma based mirror cleaning or modular approaches for frequent maintenance and exchange are being developed. Under the even stronger fluences of plasma particles, neutron/gamma and radiation loads on DEMO, durable and reliable signals for plasma control can only be obtained by selecting diagnostic methods with regard to their robustness, and retracting vulnerable front-end components into protected locations. Based on this approach, an initial DEMO D&C concept is presented, which covers all major control issues by signals to be derived from at least two different diagnostic methods (risk mitigation).
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8.
  • Croci, Gabriele, et al. (författare)
  • A high-efficiency thermal neutron detector based on thin 3D (B4C)-B-10 converters for high-rate applications
  • 2018
  • Ingår i: Europhysics letters. - : IOP PUBLISHING LTD. - 0295-5075 .- 1286-4854. ; 123:5
  • Tidskriftsartikel (refereegranskat)abstract
    • new position-sensitive thermal neutron detector based on boron-coated converters has been developed as an alternative to today's standard He-3-based technology for application to thermal neutron scattering. The key element of the development is a novel 3D (B4C)-B-10 converter which has been ad hoc designed and realized with the aim of combining a high neutron conversion probability via the B-10(n, alpha)(7) Li reaction together with an efficient collection of the produced charged particles. The developed 3D converter is composed of thin aluminium grids made by a micro-waterjet technique and coated on both sides with a thin layer of( 10)B(4)C. When coupled to a GEM detector this converter allows reaching neutron detection efficiencies close to 50% at neutron wavelengths equal to 4 angstrom. In addition, the new detector features a spatial resolution of about 5 min and can sustain counting rates well in excess of 1 MHz/cm(2). The newly developed neutron detector will enable time-resolved measurements of different kind of samples in neutron scattering experiments at high flux spallation sources and can find a use in applications where large areas and custom geometries of thermal neutron detectors are foreseen. 
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9.
  • Croci, Gabriele, et al. (författare)
  • I-BAND-GEM : a new way for improving BAND-GEM efficiency to thermal and cold neutrons
  • 2019
  • Ingår i: The European Physical Journal Plus. - 2190-5444 .- 2190-5444. ; 134:4
  • Tidskriftsartikel (refereegranskat)abstract
    • .The BAND-GEM detector represents one of the novel thermal neutron detection devices that have been developed in order to fulfil the needs of high intensity neutron sources that, like ESS (the European Spallation Source), will start operation in the next few years. The first version of this detector featured a detection efficiency of about 40% for neutrons with a wavelength of 4 angstrom, a spatial resolution of about 6mm and a rate capability in the order of some MHz/cm(2). The novelty of this device is represented by an improved 3D converter cathode (10 cm thick) based on (B4C)-B-10-coated aluminum grids positioned in a controlled gas mixture volume put on top of a Triple GEM amplifying stage. The position where the neutron interacts in the converter depends on their energy and it was observed that the first version of the detector would suffer from an efficiency decrease for long (>5 angstrom) neutron wavelength. This paper describes how the new 3D cathode allowed improving the detection efficiency at long neutron wavelengths while keeping all the benefits of the first BAND-GEM version.
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10.
  • Eriksson, Jacob, Dr, 1985-, et al. (författare)
  • Measuring fast ions in fusion plasmas with neutron diagnostics at JET
  • 2019
  • Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 61:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Fast ions in fusion plasmas often leave characteristic signatures in the neutron emission from the plasma. In this paper, we show how neutron measurements can be used to study fast ions and give examples of physics results obtained on present day tokamaks. The focus is on measurements with dedicated neutron spectrometers and with compact neutron detectors used in each channel of neutron profile monitors. A measured neutron spectrum can be analyzed in several different ways, depending on the physics scenario under consideration. Gross features of a fast ion energy distribution can be studied by applying suitably chosen thresholds to the measured spectrum, thus probing ions with different energies. With this technique it is possible to study the interaction between fast ions and MHD activity, such as toroidal Alfven eigenmodes (TAEs) and sawtooth instabilities. Quantitative comparisons with modeling can be performed by a direct computation of the neutron emission expected from a given fast ion distribution. Within this framework it is also possible to determine physics parameters, such as the supra-thermal fraction of the neutron emission, by fitting model parameters to the data. A detailed, model-independent estimate of the fast ion distribution can be obtained by analyzing the data in terms of velocity space weight functions. Using this method, fast ion distributions can be resolved in both energy and pitch by combining neutron and gamma-ray measurements obtained along several different sightlines. Fast ion measurements of the type described in this paper will also be possible at ITER, provided that the spectrometers have the dynamic range required to resolve the fast ion spectral features in the presence of the dominating thermonuclear neutron emission. A dedicated high-resolution neutron spectrometer has been designed for this purpose.
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  • Resultat 1-10 av 41
  • [1]2345Nästa

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