| 1. |
- Binda, Federico, 1987-, et al.
(författare)
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Analysis of the fast ion tails observed in the NE213pulse height specta measured during third harmonicradio-frequency heating experiments at JET
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we investigate the possibility of using a NE213 liquid scintillator as aneutron spectrometer to diagnose the fast ion tails produced in experiments with 3rd harmonicradio-frequency heating.We discuss mainly the instrumental effects that need to be considered and corrected for in orderto obtain a good agreement between measured data and models: gain drift, pile-up, impact of theassumption of a standard proton light yield function. We also address problems related to thepresence of triton burn-up events in the spectrum.The expected ion distribution is obtained from a simple 1D Fokker-Planck model. The parametersof the model are estimated using the data collected by the TOFOR neutron spectrometer.The agreement between the data and the model is good and it is possible to make a clear distinctionbetween discharges that had different electron densities and thus different cut-off energies. Wecan conclude that NE213 scintillators can provide useful spectroscopic information for this kind ofexperiments.
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| 2. |
- Eriksson, Benjamin, et al.
(författare)
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First measurement in a magnetic confinement fusion experiment of the T + T -> 5He + n intermediate two-body resonant reaction
- 2024
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 109
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first experimental measurements made at a magnetic confinement fusion device of the T + T → α + 2n reaction indicating the presence of the intermediate two-body resonant reaction T + T → ⁵He + n. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, n_T/(n_T + n_D) ≈ 0.99, heated with T neutral beam injection (NBI), were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an R-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the TT neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA.
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| 3. |
- Gatu Johnson, Maria, 1978-, et al.
(författare)
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Neutron emission from beryllium reactions in JET deuterium plasmas with 3He minority
- 2010
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:4, s. 045005-
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Tidskriftsartikel (refereegranskat)abstract
- Recent fast ion studies at JET involve ion cyclotron resonance frequency (ICRF) heating tuned to minority He-3 in cold deuterium plasmas, with beryllium evaporation in the vessel prior to the session. During the experiments, the high-resolution neutron spectrometer TOFOR was used to study the energy spectrum of emitted neutrons. Neutrons of energies up to 10MeV, not consistent with the neutron energy spectrum expected from d(d,n)He-3 reactions, were observed. In this paper, we interpret these neutrons as a first-time observation of a Be-9(He-3, n)C-11 neutron spectrum in a tokamak plasma, a conclusion based on a consistent analysis of experimental data and Monte Carlo simulations. Be-9(a, n)C-12 and Be-9(p, n)B-9 reactions are also simulated for p and a fusion products from d(He-3, a) p reactions; these two-step processes are seen to contribute on a level of about 10% of the single-step process in Be-9(He-3, n) C-11. Contributions to the total neutron yield from the Be-9(3He, n)C-11 reaction are found to be in the range 13 +/- 3 to 57 +/- 5%. We demonstrate how TOFOR can be used to simultaneously (i) probe the deuterium distribution, providing reliable measurements of the bulk deuterium temperature, here in the range 3.2 +/- 0.4 to 6.3 +/- 1.0 keV and (ii) provide an estimate of the beryllium concentration (in the range 0.48 +/- 0.17 to 6.4 +/- 1.7% of n(e) assuming T-3He = 300 keV). The observation of Be-9 related neutrons is relevant in view of the upcoming installation of a beryllium-coated ITER-like wall on JET and for ITER itself. An important implication is possible neutron-induced activation of the ITER vessel during the low-activation phase with ICRF heating tuned to minority He-3 in hydrogen plasmas.
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| 4. |
- Gatu Johnson, Maria, 1978-, et al.
(författare)
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Neutron emission levels during the ITER zero activation phase
- 2010
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:8, s. 084020-
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Tidskriftsartikel (refereegranskat)abstract
- In recent experiments at JET, a contribution to the neutron emission from reactions between beryllium and 3He, 4He and H has been identified. With the beryllium walled planned for ITER, this raises the question of possible neutron activation during the ITER zero activation phase. Here, we estimate the neutron emission rates for various heating scenarios foreseen for this ITER phase using Monte Carlo simulations. The emission is seen to be strongly dependent on the scenario chosen and the assumptions involved. We find that fundamental minority heating can contribute on the scale of low temperature deuterium plasmas, depending on minority concentration and ICRH power applied. Harmonic ICRH leads to production of tails that can give rise to significant neutron emission rates, while rates from hydrogen beams will be near zero. Better knowledge of the zero activation phase conditions, and more sophisticated ICRH codes, would be needed to give exact rate predictions. We conclude that rates from so-called zero activation plasmas will be significantly lower than expected for the DD or DT phases, but far from zero.
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| 5. |
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| 6. |
- Marcinkevicius, Benjaminas, 1989-
(författare)
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The Thin-foil Proton Recoil neutron spectrometer for DT plasmas
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent advancements in plasma physics are intensifying the demand for advanced diagnostic techniques in fusion research, particularly for the upcoming ITER fusion reactor. The ITER fusion reactor is projected to be ten times more powerful than its predecessors, imposing higher constraints on operational parameters. To meet ITER's requirements, such as the fuel ion ratio nt/nd and fuel ion temperature Ti, a High Resolution Neutron Spectrometer System (HRNS) has been proposed.This thesis focuses on the Thin-foil proton recoil (TPR) spectrometer, an integral part of the HRNS, with an emphasis on its application and validation within the ITER context. The research encompasses two main areas: spectrometer simulations and experimental validation. Through a combination of custom transport code and Geant4 simulations, the study investigates the optimization of the TPR spectrometer's design in terms of efficiency and energy resolution. Additionally, selected design performance under ITER-like conditions has been investigated. These simulations are critical in assessing the spectrometer's capabilities and limitations during operation at ITER. Subsequent experimental validation, conducted using a DT neutron generator and a TPR spectrometer prototype, verified the existing simulation framework in terms of energy resolution and background discrimination methods. We examined a Tandem neutron spectrometer, used in fusion plasma diagnostics at JET to further investigate TPR spectrometer diagnostic possibilities. Tandem spectrometer was operational during JET's first DT campaign, the spectrometer shares the neutron detection principles of the TPR. The fuel ion ratio nt/ntot was determined using the Tandem data together with inputs from PENCIL or TRANSP, for previously not analysed JET discharges. Our findings indicate that estimation of nt/ntot is feasible using either PENCIL or TRANSP. Furthermore, the research demonstrates that TPR based neutron spectrometers can be effectively used in fuel ion ratio determination. In conclusion, this research significantly advances fusion plasma diagnostics. It validates the TPR spectrometer's design in terms of energy resolution and efficiency for ITER, predicting a signal-to-background ratio of approximately 550 and a maximum count rate of 120kHz. The results from the TPR prototype experiment, replicated with the Geant4 simulation, along with comparative analysis with the JET's Tandem spectrometer, highlight the TPR spectrometer's broad applicability in fusion diagnostics, marking a major advancement in the field.
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| 7. |
- Nocente, Massimo, et al.
(författare)
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Neutron spectroscopy measurements of tritium beam transport at JET
- 2014
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 54:10, s. 104010-
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Tidskriftsartikel (refereegranskat)abstract
- A detailed description of the 14 MeV neutron emission in plasmas heated by neutral beam injection has been carried out by coupling Monte Carlo calculations of the neutron emission spectrum with TRANSP modelling of the beam ion energy distributions. The model is used to study tritium beam injection experiments of the JET trace tritium campaign for internal transport barrier (ITB) and H-mode discharges. For ITB discharges, the measured neutron emission spectrum is well described by modelling using as input the beam ion distribution calculated with TRANSP. For H mode discharges the neutron spectrum can be reproduced only if high energy tritons are lost from the plasma, suggesting the possible role of low frequency tearing modes on the beam ions. The presented results are of relevance for tritium beam transport studies in trace tritium experiments and, more generally, for deuterium and tritium transport studies in high power experiments using neutron emission spectroscopy.
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| 8. |
- Sahlberg, Arne, et al.
(författare)
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Energy and pitch distribution of RF accelerated deuterons measured with multi-sightline neutron spectroscopy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In radio-frequency (RF) heated tokamak experiments, it is important to have an accurate picture of the behavior of supra-thermal fuel ions. This paper uses neutron emission spectroscopy with dual sightlines to determine the joint energy-pitch distribution of RF accelerated deuterons at JET.The energy spectrum of neutrons emitted from reactions involving supra-thermal ions is dependent on the energy-pitch distribution of the ions, but also on the sightline at which they are measured. A sightline perpendicular to the magnetic axis is highly sensitive to energy variations, but not to variations in pitch, and vice versa for a parallel sightline. In this paper, we combine data from the time-of-flight spectrometer TOFOR, which is perpendicular, and the compact spectrometer CNS, which is partly parallel to the magnetic axis, to assess key features of the energy-pitch distribution, by fitting a parameterized model to the two sets of data simultaneously.The presented analysis method is applied to data from six JET pulses, using two distinct RF heating schemes, the third harmonic heating scheme, and the three-ion scheme. The results show that both scenarios produce a highly energetic fast-ion tail reaching into the MeV region. However, there is a significant difference in fast-ion pitch resulting from two heating schemes, specifically in that the pitch distribution of the third harmonic pulses is centered around zero, while the three-ion scenario produces a fast-ion distribution with a tail centered around pitch 0.25. This difference in pitch corroborates results from gamma-ray spectroscopy measurements and simulations with modeling codes.
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| 9. |
- Sperduti, Andrea, 1991-
(författare)
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Experimental methods of neutron diagnostics and fast ion physics for fusion devices
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of the neutron emission resulting from nuclear fusion reactions provide an abundance of information on the underlying spatial, temporal and energetic distributions of reacting ions and how they are affected by a wide range of MagnetoHydroDynamic (MHD) instabilities.This thesis focuses on studies of the neutron emission and fast ion physics at the Mega Ampere Spherical Tokamak (MAST), its upgrade MAST-U, the Joint European Torus (JET) and the Divertor Tokamak Test (DTT). In particular, measurements and simulations of neutron emissivity and neutron rates by collimated neutron flux monitor are here discussed and applied to study the properties of the plasma and of the fast ion distribution.The first part of the thesis describes plasma measurement methods based on neutron diagnostics. In particular, the design of the neutron camera upgrade on MAST-U is here presented and possible outcomes from its future measurements are discussed. MAST and MAST-U, due to their low plasma temperature, are suitable for fast ion studies and in order to relate neutron measurements with the fast ion distributions the weight functions of the neutron camera on MAST are presented. Fast ions behaviour will be studied as well on DTT where the presence of a collimated neutron flux monitor and a Time Of Flight system is envisaged. Their conceptual designs are presented here. Finally, a novel application of neutron flux monitor for measuring the plasma position is discussed and its application on JET is described here. The second part of the thesis introduces the problem with the “neutron deficit” observed on MAST and the approaches used for its resolution such as the Influence Method and the effect of the Guiding Center and Gyro-Orbit modelling on MAST. The forward modelling based on ASCOT/BBNBI, LINE21, DRESS, NRESP has been compared against the same one but based on TRANSP/NUBEAM simulations. The first modelling was used to validate neutron camera measurements on MAST reducing the observed discrepancy to values within the estimated experimental uncertainties, while the second one was used to benchmark DRESS.
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