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Träfflista för sökning "WFRF:(Bykov Igor) ;pers:(Rachlew Elisabeth)"

Sökning: WFRF:(Bykov Igor) > Rachlew Elisabeth

  • Resultat 1-10 av 317
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1.
  • Cufar, Aljaz, et al. (författare)
  • Calculations to support JET neutron yield calibration : Modelling of neutron emission from a compact DT neutron generator
  • 2017
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER. - 0168-9002 .- 1872-9576. ; 847, s. 199-204
  • Tidskriftsartikel (refereegranskat)abstract
    • At the Joint European Torus (JET) the ex-vessel fission chambers and in-vessel activation detectors are used as the neutron production rate and neutron yield monitors respectively. In order to ensure that these detectors produce accurate measurements they need to be experimentally calibrated. A new calibration of neutron detectors to 14 MeV neutrons, resulting from deuterium tritium (DT) plasmas, is planned at JET using a compact accelerator based neutron generator (NG) in which a D/T beam impinges on a solid target containing T/D, producing neutrons by DT fusion reactions. This paper presents the analysis that was performed to model the neutron source characteristics in terms of energy spectrum, angle energy distribution and the effect of the neutron generator geometry. Different codes capable of simulating the accelerator based DT neutron sources are compared and sensitivities to uncertainties in the generator's internal structure analysed. The analysis was performed to support preparation to the experimental measurements performed to characterize the NG as a calibration source. Further extensive neutronics analyses, performed with this model of the NG, will be needed to support the neutron calibration experiments and take into account various differences between the calibration experiment and experiments using the plasma as a source of neutrons.
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2.
  • Lengar, Igor, et al. (författare)
  • Activation material selection for multiple foil activation detectors in JET TT campaign
  • 2018
  • Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 136, s. 988-992
  • Tidskriftsartikel (refereegranskat)abstract
    • In the preparation for the Deuterium-Tritium campaign, JET will operate with a tritium plasma. The T + T reaction consists of two notable channels: (1) T + T -> He-4 + 2n, (2) T + T -> He-5 + n -> He-4 + 2n. The reaction channel (1) is the reaction with the highest branching ratio and a continuum of neutron energies being produced. Reaction channel (2) produces a spectrum with a peak at 8.8 MeV. A particular problem is the ratio between the individual TT reaction channels, which is highly dependent on the energy of the reacting tritium ions. There are very few measurements on the TT spectrum and the study at JET would be interesting. The work is focused on the determination of the spectral characteristics in the TT plasma discharges, especially on the presence of the 8.8 MeV peak, a consequence of channel (2) of the TT reaction. The possibility to use an optimized set of activation materials in order to target the measurement of the 8.8 MeV peak is studied. The lower limit of detection for the channel (2) ratio within the TT reaction is estimated and the influence of DT source neutrons, which are a consequence of deuterium traces in the plasma, is investigated.
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3.
  • Lengar, Igor, et al. (författare)
  • Radiation damage and nuclear heating studies in selected functional materials during the JET DT campaign
  • 2016
  • Ingår i: Fusion engineering and design. - : Elsevier. - 0920-3796 .- 1873-7196. ; 109, s. 1011-1015
  • Tidskriftsartikel (refereegranskat)abstract
    • A new Deuterium-Tritium campaign (DTE2) is planned at JET in the next years, with a proposed 14 MeV neutron budget of 1.7 x 10(21), which is nearly an order of magnitude higher than any previous DT campaigns. The neutron and gamma ray fields inside the JET device during DT plasma operations at specific locations have previously been evaluated. It is estimated that a total neutron fluence on the first wall of JET of up to 10(20) n/m(2) could be achieved, which is comparable to the fluence occurring in ITER at the end of life in the rear part of the port plug, where several diagnostic components will be located. The purpose of the present work is to evaluate the radiation damage and nuclear heating in selected functional materials to be irradiated at JET during DT plasma operation. These quantities are calculated with the use of the MCNP6 code and the FISPACT II code. In particular the neutron and gamma ray fields at specific locations inside the JET device, dedicated to material damage studies, were characterized. The emphasis is on a potential longterm irradiation station located close to the first wall at outboard midplane, offering the opportunity to irradiate samples of functional materials used in ITER diagnostics, to assess the degradation of the physical properties. The radiation damage and the nuclear heating were calculated for selected materials irradiated in these positions and for the neutron flux and fluence expected in DTE2. The studied candidate functional materials include, among others, Sapphire, YAG, ZnS, Spinel, Diamond. In addition the activation of the internal irradiation holder itself was calculated with FISPACT. Damage levels in the range of 10(-5) dpa were found. 2016 EURATOM.
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4.
  • Snoj, Luka, et al. (författare)
  • Neutronic analysis of JET external neutron monitor response
  • 2016
  • Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 109, s. 99-103
  • Tidskriftsartikel (refereegranskat)abstract
    • The power output of fusion devices is measured in terms of the neutron yield which relates directly to the fusion yield. JET made a transition from Carbon wall to ITER-Like Wall (Beryllium/Tungsten/Carbon) during 2010-11. Absolutely calibrated measurement of the neutron yield by JET neutron monitors was ensured by direct measurements using a calibrated Cf-252 neutron source (NS) deployed by the in-vessel remote handling system (RHS) inside the JET vacuum vessel. Neutronic calculations were required in order to understand the neutron transport from the source in the vacuum vessel to the fission chamber detectors mounted outside the vessel on the transformer limbs of the tokamak. We developed a simplified computational model of JET and the JET RHS in Monte Carlo neutron transport code MCNP and analyzed the paths and structures through which neutrons reach the detectors and the effect of the JET RHS on the neutron monitor response. In addition we performed several sensitivity studies of the effect of substantial massive structures blocking the ports on the external neutron monitor response. As the simplified model provided a qualitative picture of the process only, some calculations were repeated using a more detailed full 3D model of the JET tokamak. (C) 2016 EURATOM. Published by Elsevier B.V. All rights reserved.
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5.
  • Aho-Mantila, L., et al. (författare)
  • Assessment of SOLPS5.0 divertor solutions with drifts and currents against L-mode experiments in ASDEX Upgrade and JET
  • 2017
  • Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 59:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The divertor solutions obtained with the plasma edge modelling tool SOLPS5.0 are discussed. The code results are benchmarked against carefully analysed L-mode discharges at various density levels with and without impurity seeding in the full-metal tokamaks ASDEX Upgrade and JET. The role of the cross-field drifts and currents in the solutions is analysed in detail, and the improvements achieved by fully activating the drift and current terms in view of matching the experimental signals are addressed. The persisting discrepancies are also discussed.
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6.
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7.
  • Andersson Sundén, Erik, et al. (författare)
  • An assessment of nitrogen concentrations from spectroscopic measurements in the JET and ASDEX upgrade divertor
  • 2019
  • Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 18, s. 147-152
  • Tidskriftsartikel (refereegranskat)abstract
    • The impurity concentration in the tokamak divertor plasma is a necessary input for predictive scaling of divertor detachment, however direct measurements from existing tokamaks in different divertor plasma conditions are limited. To address this, we have applied a recently developed spectroscopic N II line ratio technique for measuring the N concentration in the divertor to a range of H-mode and L-mode plasma from the ASDEX Upgrade and JET tokamaks, respectively. The results from both devices show that as the power crossing the separatrix, P-sep, is increased under otherwise similar core conditions (e.g. density), a higher N concentration is required to achieve the same detachment state. For example, the N concentrations at the start of detachment increase from approximate to 2% to approximate to 9% as P-sep, is increased from approximate to 2.5 MW to approximate to 7 MW. These results tentatively agree with scaling law predictions (e.g. Goldston et al.) motivating a further study examining the parameters which affect the N concentration required to reach detachment. Finally, the N concentrations from spectroscopy and the ratio of D and N gas valve fluxes agree within experimental uncertainty only when the vessel surfaces are fully-loaded with N.
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8.
  • Angioni, C., et al. (författare)
  • Dependence of the turbulent particle flux on hydrogen isotopes induced by collisionality
  • 2018
  • Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674 .- 1070-6631 .- 1089-7666. ; 25:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact of the change of the mass of hydrogen isotopes on the turbulent particle flux is studied. The trapped electron component of the turbulent particle convection induced by collisionality, which is outward in ion temperature gradient turbulence, increases with decreasing thermal velocity of the isotope. Thereby, the lighter is the isotope, the stronger is the turbulent pinch, and the larger is the predicted density gradient at the null of the particle flux. The passing particle component of the flux increases with decreasing mass of the isotope and can also affect the predicted density gradient. This effect is however subdominant for usual core plasma parameters. The analytical results are confirmed by means of both quasi-linear and nonlinear gyrokinetic simulations, and an estimate of the difference in local density gradient produced by this effect as a function of collisionality has been obtained for typical plasma parameters at mid-radius. Analysis of currently available experimental data from the JET and the ASDEX Upgrade tokamaks does not show any clear and general evidence of inconsistency with this theoretically predicted effect outside the errorbars and also allows the identification of cases providing weak evidence of qualitative consistency.
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9.
  • Angioni, C., et al. (författare)
  • Gyrokinetic study of turbulent convection of heavy impurities in tokamak plasmas at comparable ion and electron heat fluxes
  • 2017
  • Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In tokamaks, the role of turbulent transport of heavy impurities, relative to that of neoclassical transport, increases with increasing size of the plasma, as clarified by means of general scalings, which use the ITER standard scenario parameters as reference, and by actual results from a selection of discharges from ASDEX Upgrade and JET. This motivates the theoretical investigation of the properties of the turbulent convection of heavy impurities by nonlinear gyrokinetic simulations in the experimentally relevant conditions of comparable ion and electron heat fluxes. These conditions also correspond to an intermediate regime between dominant ion temperature gradient turbulence and trapped electron mode turbulence. At moderate plasma toroidal rotation, the turbulent convection of heavy impurities, computed with nonlinear gyrokinetic simulations, is found to be directed outward, in contrast to that obtained by quasi-linear calculations based on the most unstable linear mode, which is directed inward. In this mixed turbulence regime, with comparable electron and ion heat fluxes, the nonlinear results of the impurity transport can be explained by the coexistence of both ion temperature gradient and trapped electron modes in the turbulent state, both contributing to the turbulent convection and diffusion of the impurity. The impact of toroidal rotation on the turbulent convection is also clarified.
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10.
  • Angioni, C., et al. (författare)
  • The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas
  • 2015
  • Ingår i: Physics of Plasmas. - : AMER INST PHYSICS. - 1070-664X .- 1089-7674. ; 22:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent progress in the understanding and prediction of the tungsten behaviour in the core of JET H-mode plasmas with ITER-like wall is presented. Particular emphasis is given to the impact of poloidal asymmetries of the impurity density. In particular, it is shown that the predicted reduction of temperature screening induced by the presence of low field side localization of the tungsten density produced by the centrifugal force is consistent with the observed tungsten behaviour in a JET discharge in H-mode baseline scenario. This provides first evidence of the role of poloidal asymmetries in reducing the strength of temperature screening. The main differences between plasma parameters in JET baseline and hybrid scenario discharges which affect the impact of poloidally asymmetric density on the tungsten radial transport are identified. This allows the conditions by which tungsten accumulation can be avoided to be more precisely defined.
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