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| 22. |
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| 23. |
- 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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| 27. |
- Erman, P., et al.
(författare)
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Non Franck-Condon effects in photoionization of molecular oxygen
- 2000
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Ingår i: Physica scripta. T. - 0281-1847. ; 62:4, s. 294-300
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical and experimental analysis of non Franck-Condon effects in photoionization to the b (4)Sigma(g)(-), state of O-2(+). Experimentally, by dispersing the synchrotron radiation induced O-2(+) b (4)Sigma(g)(-) a (IIu)-I-4 fluorescence we derive the b (4)Sigma(g)(-), State vibrational branching ratios in the excitation energy range 21-34 eV. The vibrational branching ratios reveal features in the region 21-28 eV indicating strong non Franck-Condon effects. The experimental results have been analysed by computing ab initio the vibrational population branching ratios using a many-body perturbation method. Additionally the autoionizing neutral states existing in this energy region have been studied. We have computed the energies of the valence states up to an energy of 30 eV their transition moments for excitations from the ground state, and autoionization rates. Our calculations show, that strong non Franck-Condon effects recorded in the branching ratio spectrum (below 25 eV) are actually caused by the narrow 3 sigma(g) --> sigma(u) shape resonance, and its coupling to the 1 pi(u) --> pi(g) channel.
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| 28. |
- 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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