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| 25. |
- Andersson Sundén, Erik, et al.
(författare)
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The thin-foil magnetic proton recoil neutron spectrometer MPRu at JET
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 610:3, s. 682-699
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Tidskriftsartikel (refereegranskat)abstract
- Neutrons are produced in fusion energy experiments with both deuterium (D) and deuterium–tritium (DT) plasmas. Neutron spectroscopy is a valuable tool in the study of the underlying fuel ion populations. The magnetic proton recoil neutron spectrometer, originally installed at JET in 1996 for 14-MeV neutron measurements, has been upgraded, with the main aim of improving its signal-to-background ratio (S/B), making measurements of the 2.5-MeV neutron emission in D plasmas possible. The upgrade includes a new focal-plane detector, based on the phoswich technique and consequently less sensitive to background, and a new custom-designed digital data acquisition system based on transient recorder cards. Results from JET show that the upgraded MPRu can measure 2.5-MeV neutrons with S/B=5, an improvement by a factor of 50 compared with the original MPR. S/B of 2.8×104 in future DT experiments is estimated. The performance of the MPRu is exemplified with results from recent D plasma operations at JET, concerning both measurements with Ohmic, ion cyclotron resonance (ICRH) and neutral beam injection (NBI) plasma heating, as well as measurements of tritium burn-up neutrons. The upgraded instrument allows for 2.5-MeV neutron emission and deuterium ion temperature measurements in plasmas with low levels of tritium, a feature necessary for the ITER experiment.
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| 26. |
- Apyan, A., et al.
(författare)
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Coherent bremsstrahlung, coherent pair production, birefringence, and polarimetry in the 20-170 GeV energy range using aligned crystals
- 2008
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Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:4, s. 041001-
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Tidskriftsartikel (refereegranskat)abstract
- The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20-170 GeV. The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences. This is significant as the theoretical description of CB and CPP is an area of active debate and development. With the approach used in this paper, both the measured cross sections and polarization observables are predicted very well. This indicates a proper understanding of CB and CPP up to energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements. New technologies for high-energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment. Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal. Our measurements and our calculations indicate low photon polarizations for the high-energy SOS photons.
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| 27. |
- Gatu Johnson, Maria, et al.
(författare)
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The 2.5-MeV neutron time-of-flight spectrometer TOFOR for experiments at JET
- 2008
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 591:2, s. 417-430
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Tidskriftsartikel (refereegranskat)abstract
- A time-of-flight (TOF) spectrometer for measurement of the 2.5-MeV neutron emission from fusion plasmas has been developed and put into use at the JET tokamak. It has been optimized for operation at high rates (TOFOR) for the purpose of performing advanced neutron emission spectroscopy (NES) diagnosis of deuterium plasmas with a focus on the fuel ion motional states for different auxiliary heating scenarios. This requires operation over a large dynamic range, including high rates of > 100 kHz with a maximum value of 0.5 MHz for the TOFOR design. This paper describes the design principles and their technical realization. The performance is illustrated with recent neutron TOF spectra recorded for plasmas subjected to different heating scenarios. A true event count rate of 39 kHz has been achieved at about a tenth of the expected neutron yield limit of JET, giving a projected maximum of 400 kHz at peak JET plasma yield. This means that the count rate capability for NES diagnosis of D plasmas has been improved more than an order of magnitude. Another important performance factor is the spectrometer bandwidth, where data have been acquired and analyzed successfully with a response function for neutrons over the energy range 1 to > 5 MeV. The implications of instrumental advancement represented by TOFOR are discussed.
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| 28. |
- Giacomelli, Luca, et al.
(författare)
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Advanced Neutron Diagnostics for JET and ITER Fusion Experiments
- 2005
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 45, s. 1191-1201
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Tidskriftsartikel (refereegranskat)abstract
- The diagnostics functions of neutron measurements as well as the roles played by neutron yield monitors, cameras and spectrometers are reviewed. The importance of recent developments in neutron emission spectroscopy (NES) diagnostics is emphasized. Results are presented from the NES diagnosis of the Joint European Torus (JET) plasmas performed with the magnetic proton recoil (MPR) spectrometer during the first deuterium tritium experiment of 1997 and the recent trace tritium experiment of 2003. The NES diagnostic capabilities at JET are presently being enhanced by an upgrade of the MPR (MPRu) and a new 2.5 MeV time-of-flight (TOF) neutron spectrometer (TOFOR). The principles of MPRu and TOFOR are described and illustrated with the diagnostic role they will play in the high performance fusion experiments in the forward programme of JET largely aimed at supporting the International Thermonuclear Experimental Reactor (ITER). The importance of the JET NES effort for ITER is discussed.
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| 29. |
- Gorini, G., et al.
(författare)
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Nuclear scattering effects on the neutron emission in fusion plasmas
- 2008
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 44:1-4, s. 57-60
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Tidskriftsartikel (refereegranskat)abstract
- Ion reactions and elastic scatterings in fusion plasmas of H and He nuclides are discussed as they can be observed in the neutron emission spectrum (NES). New calculations are presented on radio-frequency driven multi-step processes in (HeD)-He-3 plasmas involving knock-on scattering whose relative importance is discussed besides use for new plasma studies.
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| 30. |
- Hellesen, Carl, et al.
(författare)
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Validation of TRANSP Simulations Using Neutron emission Spectroscopy with Dual Sight Lines
- 2008
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:10, s. 10E510-
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Tidskriftsartikel (refereegranskat)abstract
- A method to generate modeled neutron spectra from bulk and fast ion distributions simulated by TRANSP has been developed. In this paper, modeled data generated from fuel ion distrubutions modeled with TRANSP is compared to measured data from two neutron spectrometers with different lines of sight; TOFOR with a radial one and the MPRu with a tangential one. The information obtained from the analysis of the measured neutron spectra such as the relative intensity of the emission from different ion populations places additional constraints on the simulation and can be used to adjust the parameters of the simulation.
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