| 1. |
- Hellesen, Carl, 1980-, et al.
(författare)
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Neutron emission generated by fast deuterons accelerated with ion cyclotron heating at JET
- 2010
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:2
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, the neutron emission from JET plasmas heated with combined deuterium neutral beam injection and third harmonic ion cyclotron radio frequency heating have been studied with neutron emission spectroscopy (NES). Very high DD neutron rates were observed with only modest external heating powers, which was attributed to acceleration of deuterium beam ions to energies of about 2-3 MeV, where the DD reactivity is on a par of that of the DT reaction. Fast deuterium energy distributions were derived from analysis of NES data and confirm acceleration of deuterium beam ions up to energies around 3 MeV, in agreement with theoretical predictions. The high neutron rates allowed for observations of changes in the fast deuterium populations on a time scale of 50 ms. Correlations were seen between fast deuterium ions at different energies and magnetohydrodynamic activities, such as monster sawtooth crashes and toroidal Alfven eigenmodes.
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| 2. |
- Hellesen, Carl, et al.
(författare)
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Fast-ion distributions from third harmonic ICRF heating studied with neutron emission spectroscopy
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:11, s. 113009-
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Tidskriftsartikel (refereegranskat)abstract
- The fast-ion distribution from third harmonic ion cyclotron resonance frequency (ICRF) heating on the Joint European Torus is studied using neutron emission spectroscopy with the time-of-flight spectrometer TOFOR. The energy dependence of the fast deuteron distribution function is inferred from the measured spectrum of neutrons born in DD fusion reactions, and the inferred distribution is compared with theoretical models for ICRF heating. Good agreements between modelling and measurements are seen with clear features in the fast-ion distribution function, that are due to the finite Larmor radius of the resonating ions, replicated. Strong synergetic effects between ICRF and neutral beam injection heating were also seen. The total energy content of the fast-ion population derived from TOFOR data was in good agreement with magnetic measurements for values below 350 kJ.
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| 3. |
- Hellesen, Carl, 1980-, et al.
(författare)
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Measurements of fast ions and their interactions with MHD activity using neutron emission spectroscopy
- 2010
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:8, s. 084006-
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Tidskriftsartikel (refereegranskat)abstract
- Ion cyclotron radio frequency (ICRF) heating can produce fast ion populations with energies reaching up to several megaelectronvolts. Here, we present unique measurements of fast ion distributions from an experiment with 3rd harmonic ICRF heating on deuterium beams using neutron emission spectroscopy (NES). From the experiment, very high DD neutron rates were observed, using only modest external heating powers. This was attributed to acceleration of deuterium beam ions to energies up to about 2-3 MeV, where the DD reactivity is on a par with that of the DT reaction. The high neutron rates allowed for observations of changes in the fast deuterium energy distribution on a time scale of 50 ms. Clear correlations were seen between fast deuterium ions in different energy ranges and magnetohydrodynamic activities, such as monster sawteeth and toroidal Alfven eigen modes (TAE). Specifically, NES data showed that the number of deuterons in the region between 1 and 1.5 MeV were decaying significantly during strong TAE activity, while ions with lower energies around 500 keV were not affected. This was attributed to resonances with the TAE modes.
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| 4. |
- Nocente, M., et al.
(författare)
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High-resolution gamma ray spectroscopy measurements of the fast ion energy distribution in JET He-4 plasmas
- 2012
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 52:6, s. 063009-
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution gamma-ray measurements were carried out on the Joint European Torus (JET) in an experiment aimed at accelerating He-4 ions in the MeV range by coupling third harmonic radio frequency heating to an injected He-4 beam. For the first time, Doppler broadening of gamma-ray peaks from the C-12(d, p gamma)C-13 and Be-9(alpha, n gamma)C-12 reactions was observed and interpreted with dedicated Monte Carlo codes based on the detailed nuclear physics of the processes. Information on the confined He-4 and deuteron energy distribution was inferred, and confined He-4 ions with energies as high as 6 MeV were assessed. A signature of MHD activity in gamma-ray traces was also detected. The reported results have a bearing on diagnostics for fast ions in the MeV range in next step fusion devices.
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| 5. |
- Tardocchi, M., et al.
(författare)
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Modeling of neutron emission spectroscopy in JET discharges with fast tritons from (T)D ion cyclotron heating
- 2006
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 77:12
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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 (T-HE). This article addresses to what extent the T-HE 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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| 6. |
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| 7. |
- 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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| 8. |
- Eriksson, Jacob, et al.
(författare)
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Finite Larmor radii effects in fast ion measurements with neutron emission spectrometry
- 2013
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:1, s. 015008-
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Tidskriftsartikel (refereegranskat)abstract
- When analysing data from fast ion measurements it is normally assumed that the gyro-phase distribution of the ions is isotropic within the field of view of the measuring instrument. This assumption is not valid if the Larmor radii of the fast ions are comparable to—or larger than—the gradient scale length in the spatial distribution of the ions, and if this scale length is comparable to—or smaller than—the width of the field of view of the measuring instrument. In this paper the effect of such an anisotropy is demonstrated by analysing neutron emission spectrometry data from a JET experiment with deuterium neutral beams together with radiofrequency heating at the third harmonic of the deuterium cyclotron frequency. In the experiment, the neutron time-of-flight spectrometer TOFOR was used to measure the neutrons from the d(d,n) 3 He-reaction. Comparison of the experimental data with Monte Carlo calculations shows that the finite Larmor radii of the fast ions need to be included in the modelling to get a good description of the data. Similar effects are likely to be important for other fast ion diagnostics, such as γ -ray spectroscopy and neutral particle analysis, as well.
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| 9. |
- Gatu Johnson, Maria, et al.
(författare)
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Modelling and TOFOR measurements of scattered neutrons at JET
- 2010
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 52:8, s. 085002-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the scattered and direct neutron fluxes in the line of sight (LOS) of the TOFOR neutron spectrometer at JET are simulated and the simulations compared with measurement results. The Monte Carlo code MCNPX is used in the simulations, with a vessel material composition obtained from the JET drawing office and neutron emission profiles calculated from TRANSP simulations of beam ion density profiles. The MCNPX simulations show that the material composition of the scattering wall has a large effect on the shape of the scattered neutron spectrum. Neutron source profile shapes as well as radial and vertical source displacements in the TOFOR LOS are shown to only marginally affect the scatter, while having a larger impact on the direct neutron flux. A matrix of simulated scatter spectra for mono-energetic source neutrons is created which is folded with an approximation of the source spectrum for each JET pulse studied to obtain a scatter component for use in the data analysis. The scatter components thus obtained are shown to describe the measured data. It is also demonstrated that the scattered flux is approximately constant relative to the total neutron yield as measured with the JET fission chambers, while there is a larger spread in the direct flux, consistent with simulations. The simulated effect on the integrated scattered/direct ratio of an increase with movements outward along the radial direction and a drop at higher values of the vertical plasma position is also reproduced in the measurements. Finally, the quantitative agreement found in scatter/direct ratios between simulations (0.185 ± 0.005) and measurements (0.187 ± 0.050) serves as a solid benchmark of the MCNPX model used.
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| 10. |
- 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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