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Sökning: WFRF:(Sjöstrand H)

  • Resultat 11-20 av 88
  • Föregående 1[2]34567...9Nästa
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  • Lanctot, M. J., et al. (författare)
  • Impact of toroidal and poloidal mode spectra on the control of non-axisymmetric fields in tokamaks
  • 2017
  • Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 24:5
  • Tidskriftsartikel (refereegranskat)abstract
    • In several tokamaks, non-axisymmetric magnetic field studies show that applied magnetic fields with a toroidal harmonic n = 2 can lead to disruptive n = 1 locked modes. In Ohmic plasmas, n = 2 magnetic reconnection thresholds in otherwise stable discharges are readily accessed at edge safety factors q similar to 3, low density, and low rotation. Similar to previous studies with n = 1 fields, the thresholds are correlated with the "overlap" field computed with the IPEC code. The overlap field quantifies the plasma-mediated coupling of the external field to the resonant field. Remarkably, the "critical overlap fields" at which magnetic islands form are similar for applied n = 1 and 2 fields. The critical overlap field increases with plasma density and edge safety factor but is independent of the toroidal field. Poloidal harmonics m> nq dominate the drive for resonant fields while m < nq harmonics have a negligible impact. This contrasts with previous results in H-mode discharges at high plasma pressure in which the toroidal angular momentum is sensitive to low poloidal harmonics. Together, these results highlight unique requirements for n > 1 field control including the need for multiple rows of coils to control selected plasma parameters for specific functions (e.g., rotation control or ELM suppression).
  • Litaudon, X., et al. (författare)
  • 14 MeV calibration of JET neutron detectors-phase 1: Calibration and characterization of the neutron source
  • 2018
  • Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 58:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is 10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e.The neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within ± 5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances.
  • Maggi, C. F., et al. (författare)
  • Studies of the pedestal structure and inter-ELM pedestal evolution in JET with the ITER-like wall
  • 2017
  • Ingår i: Nuclear Fusion. - EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England. [Maggi, C. F.; Saarelma, S.; Flanagan, J.; Lupelli, I.; Pamela, S.; Garzotti, L.; Lerche, E.; Rimini, F.] Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England. [Frassinetti, L.] KTH, Fus Plasma Phys, Assoc VR, SE-10044 Stockholm, Sweden. [Horvath, L.; Lunniss, A.; Wilson, H.; Leyland, M.] Univ York, York Plasma Inst, Dept Phys, York YO10 5DD, N Yorkshire, England. [Urano, H.] Natl Inst QST, Naka, Ibaraki 3110193, Japan. [Nunes, I.] Inst Super Tecn, Assoc IST, Av Rovisco Pais, P-1049001 Lisbon, Portugal. : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The pedestal structure of type I ELMy H-modes has been analysed for JET with the ITER-like Wall (JET-ILW). The electron pressure pedestal width is independent of rho* and increases proportionally to root beta(pol,PED). Additional broadening of the width is observed, at constant beta(pol, PED), with increasing nu* and/ or neutral gas injection and the contribution of atomic physics effects in setting the pedestal width cannot as yet be ruled out. Neutral penetration alone does not determine the shape of the edge density profile in JET-ILW. The ratio of electron density to electron temperature scale lengths in the edge transport barrier region, eta(e), is of order 2-3 within experimental uncertainties. Existing understanding, represented in the stationary linear peeling-ballooning mode stability and the EPED pedestal structure models, is extended to the dynamic evolution between ELM crashes in JET-ILW, in order to test the assumptions underlying these two models. The inter-ELM temporal evolution of the pedestal structure in JET-ILW is not unique, but depends on discharge conditions, such as heating power and gas injection levels. The strong reduction in (pe,PED) with increasing D-2 gas injection at high power is primarily due to clamping of del T-e half way through the ELM cycle and is suggestive of turbulence limiting the T-e pedestal growth. The inter-ELM pedestal pressure evolution in JET-ILW is consistent with the EPED model assumptions at low gas rates and only at low beta at high gas rates. At higher beta and high gas rate the inter-ELM pedestal pressure evolution is qualitatively consistent with the kinetic ballooning mode (KBM) constraint but the peeling-ballooning (P-B) constraint is not satisfied and the ELM trigger mechanism remains as yet unexplained.
  • Rochman, Dimitri, et al. (författare)
  • The TENDL library : Hope, reality and future
  • 2017
  • Ingår i: Nd 2016 Bruges. - Les Ulis : EDP Sciences. - 9782759890200
  • Konferensbidrag (refereegranskat)abstract
    • The TALYS Evaluated Nuclear Data Library (TENDL) has now 8 releases since 2008. Considerable experience has been acquired for the production of such general-purpose nuclear data library based on the feedback from users, evaluators and processing experts. The backbone of this achievement is simple and robust: completeness, quality and reproducibility. If TENDL is extensively used in many fields of applications, it is necessary to understand its strong points and remaining weaknesses. Alternatively, the essential knowledge is not the TENDL library itself, but rather the necessary method and tools, making the library a side product and focusing the efforts on the evaluation knowledge. The future of such approach will be discussed with the hope of nearby greater success.
  • Adolfsson, J., et al. (författare)
  • QCD challenges from pp to A–A collisions
  • 2020
  • Ingår i: European Physical Journal A. - : Springer. - 1434-6001. ; 56:11
  • Forskningsöversikt (refereegranskat)abstract
    • This paper is a write-up of the ideas that were presented, developed and discussed at the third International Workshop on QCD Challenges from pp to A–A, which took place in August 2019 in Lund, Sweden (Workshop link: https://indico.lucas.lu.se/event/1214/). The goal of the workshop was to focus on some of the open questions in the field and try to come up with concrete suggestions for how to make progress on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.
  • Aiba, N., et al. (författare)
  • Numerical analysis of ELM stability with rotation and ion diamagnetic drift effects in JET
  • 2017
  • Ingår i: Nuclear Fusion. - EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England. [Aiba, N.] Natl Inst Quantum & Radiol Sci & Technol, Rokkasho, Aomori 0393212, Japan. [Giroud, C.; Saarelma, S.; Lupelli, I.; Casson, F. J.; Pamela, S.; Maggi, C. F.] Culham Ctr Fus Energy, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England. [Honda, M.; Urano, H.] Natl Inst Quantum & Radiol Sci & Technol, Naka, Ibaraki 3110193, Japan. [Delabie, E.] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA. [Frassinetti, L.] KTH, Div Fus Plasma Phys, SE-10041 Stockholm, Sweden. : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Stability to the type-I edge localized mode (ELM) in JET plasmas was investigated numerically by analyzing the stability to a peeling-ballooning mode with the effects of plasma rotation and ion diamagnetic drift. The numerical analysis was performed by solving the extended Frieman-Rotenberg equation with the MINERVA-DI code. To take into account these effects in the stability analysis self-consistently, the procedure of JET equilibrium reconstruction was updated to include the profiles of ion temperature and toroidal rotation, which are determined based on the measurement data in experiments. With the new procedure and MINERVA-DI, it was identified that the stability analysis including the rotation effect can explain the ELM trigger condition in JET with ITER like wall (JET-ILW), though the stability in JET with carbon wall (JET-C) is hardly affected by rotation. The key difference is that the rotation shear in JET-ILW plasmas analyzed in this study is larger than that in JET-C ones, the shear which enhances the dynamic pressure destabilizing a peeling-ballooning mode. In addition, the increase of the toroidal mode number of the unstable MHD mode determining the ELM trigger condition is also important when the plasma density is high in JET-ILW. Though such modes with high toroidal mode number are strongly stabilized by the ion diamagnetic drift effect, it was found that plasma rotation can sometimes overcome this stabilizing effect and destabilizes the peeling-ballooning modes in JET-ILW.
  • Alhassan, E., et al. (författare)
  • Bayesian updating for data adjustments and multi-level uncertainty propagation within Total Monte Carlo
  • 2020
  • Ingår i: Annals of Nuclear Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0306-4549 .- 1873-2100. ; 139
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, a method is proposed for combining differential and integral benchmark experimental data within a Bayesian framework for nuclear data adjustments and multi-level uncertainty propagation, using the Total Monte Carlo method. First, input parameters to basic nuclear physics models implemented within the TALYS code, were randomly varied to produce a large set of random nuclear data files. Next, a probabilistic data assimilation was carried out by computing the likelihood function for each random nuclear data file based first on only differential experimental data and then on integral benchmark data. The individual likelihood functions from the two updates were then combined into a global likelihood function. The proposed method was applied for the adjustment of n+Pb-208 in the fast energy region below 20 MeV. The adjusted file was compared with available experimental data as well as evaluations from the major nuclear data libraries and found to compare favourably.
  • Alwall, J., et al. (författare)
  • A standard format for Les Houches Event Files
  • 2007
  • Ingår i: Computer Physics Communications. - : Elsevier. - 0010-4655. ; 176:4, s. 300-304
  • Tidskriftsartikel (refereegranskat)abstract
    • A standard file format is proposed to store process and event information, primarily output from partoti-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.
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