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Sökning: WFRF:(Giacomelli Luca)

  • Resultat 41-49 av 49
  • Föregående 1234[5]
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41.
  • Sjöstrand, Henrik, et al. (författare)
  • Gain stabilization control system of the upgraded magnetic protonrecoil neutron spectrometer at JET
  • 2009
  • Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 80:6, s. 063505-
  • Tidskriftsartikel (refereegranskat)abstract
    • Burning plasma experiments such as ITER and DEMO require diagnostics capable of withstanding the harsh environment generated by the intense neutron flux and to maintain stable operating conditions for times longer than present day systems. For these reasons, advanced control and monitoring (CM) systems will be necessary for the reliable operation of diagnostics. This paper describes the CM system of the upgraded magnetic proton recoil neutron spectrometer installed at the Joint European Torus focusing in particular on a technique for the stabilization of the gain of the photomultipliers coupled to the neutron detectors. The results presented here show that this technique provides good results over long time scales. The technique is of general interest for all diagnostics that employ scintillators coupled to photomultiplier tubes.
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42.
  • Sjöstrand, Henrik, et al. (författare)
  • Gain stabilization control system of the upgraded magneticproton recoil neutron spectrometer at JET
  • 2009
  • Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 80:6, s. 063505-
  • Tidskriftsartikel (refereegranskat)abstract
    • Burning plasma experiments such as ITER and DEMO require diagnostics capable of withstanding the harsh environment generated by the intense neutron flux and to maintain stable operating conditions for times longer than present day systems. For these reasons, advanced control and monitoring (CM) systems will be necessary forthe reliable operation of diagnostics. This paper describes the CM system of theupgraded magnetic proton recoil neutron spectrometer installed at the Joint European Torus focusing in particular on a technique for the stabilization of the gain of thephotomultipliers coupled to the neutron detectors. The results presented here show that this technique provides good results over long time scales. The technique is of general interest for all diagnostics that employ scintillators coupled to photomultiplier tubes.
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43.
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44.
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45.
  • Sjöstrand, Henrik, et al. (författare)
  • Triton burn-up neutron emission in JET low current plasmas
  • 2008
  • Ingår i: Journal of Physics D. - 0022-3727 .- 1361-6463. ; 41:11, s. 115208-
  • Tidskriftsartikel (refereegranskat)abstract
    • The 14 MeV neutron emission from JET deuterium discharges is analysed on the basis of the information on all neutron diagnostics available on JET. This emission is due to the d + t → α + n reaction, mainly, the triton burn-up process, and is used to determine the fast triton confinement. A simplified model for triton burn-up neutron emission has been used and provides an adequate description of the 14 MeV emission. First orbit triton losses are found to amount to 50%, 20% and 10% at Ip = 1 MA, 2 MA and 3 MA, respectively. Neutron emission spectroscopy measurements with the magnetic proton recoil neutron spectrometer have detected a contribution to the 14 MeV emission due to residual tritium. For the selected (low impurity) discharges analysed in this paper 15% of the 14 MeV emission comes from the residual tritium reactions. It is also found that the residual tritium concentration tends to increase with increasing impurity content.
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46.
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47.
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48.
  • Tardocchi, M., et al. (författare)
  • Modeling of neutron emission spectroscopy in JET discharges with fast tritons from (T)D ion cyclotron heating
  • 2006
  • Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 77:12, s. 126107-
  • Tidskriftsartikel (refereegranskat)abstract
    • The measurement of fast ion populations is one of the diagnostic capabilities provided by neutron emission spectroscopy (NES). NES measurements were carried out during JET trace tritium campaign with the magnetic proton recoil neutron spectrometer. A favorable plasma scenario is (T)D where the resulting 14 MeV neutron yield is dominated by suprathermal emission from energetic tritons accelerated by radio frequency at their fundamental cyclotron frequency. Information on the triton distribution function has been derived from NES data with a simple model based on two components referred to as bulk (B) and high energy (HE). The HE component is based on strongly anisotropic tritium distribution that can be used for routine best-fit analysis to provide tail temperature values (THE). This article addresses to what extent the THE values are model dependent by comparing the model above with a two-temperature (bi-) Maxwellian model featuring parallel and perpendicular temperatures. The bi-Maxwellian model is strongly anisotropic and frequently used for radio frequency theory.
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49.
  • Van Eester, Dirk, et al. (författare)
  • JET (3He)–D scenarios relying on RF heating: survey of selected recent experiments
  • 2009
  • Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 51:4, s. 044007-
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent JET experiments have been devoted to the study of (3He)–D plasmas involving radio frequency (RF) heating. This paper starts by discussing the RF heating efficiency theoretically expected in such plasmas, covering both relevant aspects of wave and of particle dynamics. Then it gives a concise summary of the main conclusions drawn from recent experiments that were either focusing on studying RF heating physics aspects or that were adopting RF heating as a tool to study plasma behavior. Depending on the minority concentration chosen, different physical phenomena are observed. At very low concentration (X[3He] < 1%), energetic tails are formed which trigger MHD activity and result in loss of fast particles. Alfvén cascades were observed and gamma ray tomography indirectly shows the impact of sawtooth crashes on the fast particle orbits. Low concentration (X[3He] < 10%) favors minority heating while for X[3He]  10% electron mode conversion damping becomes dominant. Evidence for the Fuchs et al standing wave effect (Fuchs et al 1995 Phys. Plasmas 2 1637–47) on the absorption is presented. RF induced deuterium tails were observed in mode conversion experiments with large X[3He] (≈18%). As tentative modeling shows, the formation of these tails can be explained as a consequence of wave power absorption by neutral beam particles that efficiently interact with the waves well away from the cold D cyclotron resonance position as a result of their substantial Doppler shift. As both ion and electron RF power deposition profiles in (3He)–D plasmas are fairly narrow—giving rise to localized heat sources—the RF heating method is an ideal tool for performing transport studies. Various of the experiments discussed here were done in plasmas with internal transport barriers (ITBs). ITBs are identified as regions with locally reduced diffusivity, where poloidal spinning up of the plasma is observed. The present know-how on the role of RF heating for impurity transport is also briefly summarized.
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  • Resultat 41-49 av 49
  • Föregående 1234[5]
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