| 1. |
- Andersson Sundén, Erik, 1979-
(author)
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Neutron Spectrometry Techniques for Fusion Plasmas : Instrumentation and Performance
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Neutron are emitted from a deuterium plasma with energies around 2.5 MeV. The neutron spectrum is intimately related to the ion velocity distribution of the plasma. As a consequence, the analysis of neutron energy spectra can give information of the plasma rotation, the ion temperature, heating efficiency and fusion power. The upgraded magnetic proton recoil spectrometer (MPRu), based on the thin-foil technique, is installed at the tokamak JET. The upgrade of the spectrometer was done to allow for measurements of deuterium plasmas. This thesis describes the hardware, the data reduction scheme and the kind of fusion plasma parameters that can be estimated from the data of the MPRu. The MPRu data from 3rd harmonic ion cyclotron resonance and beam heating are studied. Other neutron spectrometer techniques are reviewed as well, in particular in the aspect of suitability for neutron emission spectrometry at ITER. Each spectrometer technique is evaluated using synthetic data which is obtained from standard scenarios of ITER. From this evaluation, we conclude that the thin-foil technique is the best technique to measure, e.g., the ion temperature in terms of time resolution.
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| 2. |
- Eriksson, Benjamin, 1992-
(author)
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The evolution of TOFu : Developing and utilizing neutron time-of-flight spectrometry of deuterium and tritium fusion plasmas at JET
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Considerable effort has been invested in attempting to generate electricity from the energy released in controlled thermonuclear fusion reactions, with a European fusion research roadmap stretching beyond 2050. Our current endeavors may culminate in a virtually inexhaustible, low-carbon energy source for future generations. Experimental reactors such as the Joint European Torus (JET) and the International Thermonuclear Experimental Reactor (ITER) are stepping stones on the road to demonstrating the viability of fusion energy. Using various diagnostics and simulations, information on the plasma conditions in such experimental reactors can be obtained.In this thesis, the neutron time-of-flight spectrometer TOFOR at JET is used to study the neutron emission spectrum from the JET machine to determine different fusion plasma parameters. The first part of the thesis describes the efforts to upgrade the data acquisition (DAQ) system of TOFOR with a new, fully digital system: TOFu. Data reduction techniques are developed for the new DAQ system, and are shown to increase the signal-to-background ratio significantly. The instrumental response function is improved using the new system by measuring the energy-dependent time resolution and energy thresholds and applying them to the response function. Data analysis routines are developed to generate time-of-flight spectra from the data acquired by the 37 TOFOR sub-detectors.In the second part of the thesis, the data acquired by the new DAQ system is used to perform various physics studies of JET plasmas. We demonstrate the possibility of measuring the fuel ion temperature for Ohmic discharges of pure deuterium plasmas, with a precision that was unattainable with the former DAQ system. Furthermore, during the time of my doctoral studies, two deuterium-tritium experimental campaigns (DTE2 and DTE3) were conducted at JET. In order to contribute to the analysis of these experiments, we developed methods to measure the tritium fuel concentration in the fusion plasma using TOFOR. Also, experiments with pure tritium plasmas gave us the unique opportunity to measure the neutron emission spectrum from the T + T4He + 2n reaction during which we made the first observation in a magnetically confined plasma of the intermediate resonant reaction T + T5He + n.The analysis methods and experimental techniques developed in this thesis may be used in future neutron spectrometry systems, e.g., at ITER where there are plans to build a high-resolution neutron spectrometer (HRNS) consisting of several detection systems, one of which is a TOFOR-like time-of-flight spectrometer.
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| 3. |
- Eriksson, Jacob
(author)
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Neutron Emission Spectrometry for Fusion Reactor Diagnosis : Method Development and Data Analysis
- 2015
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Doctoral thesis (other academic/artistic)abstract
- It is possible to obtain information about various properties of the fuel ions deuterium (D) and tritium (T) in a fusion plasma by measuring the neutron emission from the plasma. Neutrons are produced in fusion reactions between the fuel ions, which means that the intensity and energy spectrum of the emitted neutrons are related to the densities and velocity distributions of these ions.This thesis describes different methods for analyzing data from fusion neutron measurements. The main focus is on neutron spectrometry measurements, using data used collected at the tokamak fusion reactor JET in England. Several neutron spectrometers are installed at JET, including the time-of-flight spectrometer TOFOR and the magnetic proton recoil (MPRu) spectrometer.Part of the work is concerned with the calculation of neutron spectra from given fuel ion distributions. Most fusion reactions of interest – such as the D + T and D + D reactions – have two particles in the final state, but there are also examples where three particles are produced, e.g. in the T + T reaction. Both two- and three-body reactions are considered in this thesis. A method for including the finite Larmor radii of the fuel ions in the spectrum calculation is also developed. This effect was seen to significantly affect the shape of the measured TOFOR spectrum for a plasma scenario utilizing ion cyclotron resonance heating (ICRH) in combination with neutral beam injection (NBI).Using the capability to calculate neutron spectra, it is possible to set up different parametric models of the neutron emission for various plasma scenarios. In this thesis, such models are used to estimate the fuel ion density in NBI heated plasmas and the fast D distribution in plasmas with ICRH.
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| 4. |
- Hellesen, Carl, 1980-
(author)
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Diagnosing Fuel Ions in Fusion Plasmas using Neutron Emission Spectroscopy
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Neutron emission spectra, measured with the time of flight spectrometer TOFOR, at the joint European torus (JET) are presented in this thesis. TOFOR has been in use since 2005, routinely measuring the neutron emission from JET plasmas. The work in the thesis mainly concerns the modeling of the signatures in the neutron spectrum that reveal different parts of the fuel ion distribution, such as the thermal bulk plasma as well as energetic ions from neutral beam and ion cyclotron heating. Parametric models of the signatures, using plasma parameters as input, are employed to generate trial neutron spectra. The parameters, such as the fuel ion temperature or the fast ion distribution function, are deduced by iteratively fitting the trial spectra to the measured data. Measurements with TOFOR have been made and the models were applied. The studies are mainly on neutrons from d(d, n)3 He reactions(DD), although the emission from reactions with the plasma impurity 9 Be and triton burn up is covered as well. This has allowed for detailed studies of e.g. the physics ICRF heating as well as the interactions between energetic ions and plasma instabilities, such as toroidal Alfvé Eigenmodes.
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| 5. |
- Sahlberg, Arne
(author)
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Multi-sightline neutron emission spectroscopy of D and T fusion plasmas at JET
- 2021
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Doctoral thesis (other academic/artistic)abstract
- An analysis of the neutron emission from a fusion plasma can be used to determine plasma properties and diagnose fusion performance. In this thesis, several analysis methods for neutron spectroscopy are presented and applied to data from the experimental fusion device JET. JET has numerous instruments for neutron measurements installed, and data from several of them are used in this thesis.The work presented here describes how various plasma parameters affect the neutron emission and how this information can be used to determine properties of the fusion plasma. Forward fitting of models parameterized in terms of the relevant plasma properties are a central part of most of the analysis methods and are used to determine key features of supra-thermal (“fast”) ion distributions for prediction of plasma performance in deuterium-tritium (d-t) experiments, and to determine the branching ratio for the formation of a short-lived 5He resonance in t+t reactions. The thesis also includes work concerning uncertainty quantification of the modeling of the neutron emission rate and the calculation of pile-up distortion of light-yield spectra from liquid scintillator detectors.A major contribution of this thesis is the novel methods for measuring properties of a fast-ion distribution using neutron spectroscopy with multiple sightlines. The combination of data from instruments viewing different parts of the plasma and/or with different viewing angles permits us to study fast-ion behavior in a more consistent and detailed fashion than if we analyze each measurement separately. Another interesting result is the first-ever observation of the neutron spectrum from t+t reactions in a magnetically confined fusion plasma, from which we can learn important things about the t+t reaction in reactor relevant conditions.
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