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Neutron Emission Spectrometry for Fusion Reactor Diagnosis: Method Development and Data Analysis
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 92 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1244
Keyword [en]
fusion, plasma diagnostics, neutron spectrometry, TOFOR, MPRu, tokamak, JET, fast ions, fuel ion density, relativistic kinematics
National Category
Fusion, Plasma and Space Physics Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-247994ISBN: 978-91-554-9217-5 (print)OAI: oai:DiVA.org:uu-247994DiVA: diva2:798599
Public defence
2015-05-22, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-04-27 Created: 2015-03-25 Last updated: 2015-07-07
List of papers
1. Calculating fusion neutron energy spectra from arbitrary reactant distributions
Open this publication in new window or tab >>Calculating fusion neutron energy spectra from arbitrary reactant distributions
2016 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 199, 40-46 p.Article in journal (Refereed) Published
Abstract [en]

The Directional Relativistic Spectrum Simulator (DRESS) code can perform Monte-Carlo calculations of reaction product spectra from arbitrary reactant distributions, using fully relativistic kinematics. The code is set up to calculate energy spectra from neutrons and alpha particles produced in the D(d, n)3He and T(d, n)4He fusion reactions, but any two-body reaction can be simulated by including the corresponding cross section. The code has been thoroughly tested. The kinematics calculations have been benchmarked against the kinematics module of the ROOT Data Analysis Framework. Calculated neutron energy spectra have been validated against tabulated fusion reactivities and against an exact analytical expression for the thermonuclear fusion neutron spectrum, with good agreement. The DRESS code will be used as the core of a detailed synthetic diagnostic framework for neutron measurements at the JET and MAST tokamaks.

Keyword
neutron energy spectra, relativistic kinematics
National Category
Fusion, Plasma and Space Physics Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-247991 (URN)10.1016/j.cpc.2015.10.010 (DOI)000367113200006 ()
Available from: 2015-03-25 Created: 2015-03-25 Last updated: 2017-12-04Bibliographically approved
2. Neutron emission from a tritium rich fusion plasma: simulations in view of a possible future d-t campaign at JET
Open this publication in new window or tab >>Neutron emission from a tritium rich fusion plasma: simulations in view of a possible future d-t campaign at JET
2012 (English)In: 39th EPS Conference on Plasma Physics 2012 (EPS 2012): Europhysics Conference Abstracts, 2012Conference paper, Published paper (Other academic)
Abstract [en]

 Neutron energy spectra from the t(t,2n)4He (t-t) reaction has been calculated for different fuel ion distributions, in order to assess the possibility to use this reaction when analyzing neutron spectrometry data from plasmas with very high tritium fraction. The shape of the neutron spectrum is determined by three-body kinematics, and is modified by interactions between the reaction products, primarily between the neutron and the 4He. The results indicate that the analysis of a t-t spectrum will be more challenging than for the d-t and d-d reactions. However, for fast ions in the MeV range, produced e.g. by harmonic radiofrequency heating and neutral beam injection, it should still be possible to obtain fast ion information from the neutron spectrum.

Keyword
nuclear fusion, neutron spectrometry, fast ions
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-192532 (URN)
Conference
39th EPS Conference on Plasma Physics 2012, EPS 2012, 2 - 6 July 2012, Stockholm, Sweden
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2016-01-25
3. Fuel ion ratio determination in NBI heated deuterium tritium fusion plasmas at JET using neutron emission spectrometry
Open this publication in new window or tab >>Fuel ion ratio determination in NBI heated deuterium tritium fusion plasmas at JET using neutron emission spectrometry
Show others...
2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 2, 023005Article in journal (Refereed) Published
Abstract [en]

The fuel ion ratio ( n t / n d ) is of central importance for the performance and control of a future burning fusion plasma, and reliable measurements of this quantity are essential for ITER. This paper demonstrates a method to derive the core fuel ion ratio by comparing the thermonuclear and beam-thermal neutron emission intensities, using a neutron spectrometer. The method is applied to NBI heated deuterium tritium (DT) plasmas at JET, using data from the magnetic proton recoil spectrometer. The trend in the results is consistent with Penning trap measurements of the fuel ion ratio at the edge of the plasma, but there is a discrepancy in the absolute values, possibly owing to the fact that the two measurements are weighted towards different parts of the plasma. It is suggested to further validate this method by comparing it to the traditionally proposed method to estimate n t / n d from the ratio of the thermal DD and DT neutron emission components. The spectrometer requirements for measuring n t / n d at ITER are also briefly discussed.

National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-244352 (URN)10.1088/0029-5515/55/2/023005 (DOI)000348843100006 ()
Available from: 2015-02-16 Created: 2015-02-16 Last updated: 2017-12-04Bibliographically approved
4. Deuterium density profile determination at JET using a neutron camera and a neutronspectrometer
Open this publication in new window or tab >>Deuterium density profile determination at JET using a neutron camera and a neutronspectrometer
Show others...
2014 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 11, 11E106- p.Article in journal (Refereed) Published
Abstract [en]

In this work we estimate the fuel ion density profile in deuterium plasmas at JET, using the JET neutron camera, the neutron time-of-flight spectrometer TOFOR, and fusion reactivities modeled by the transport code TRANSP. The framework has been tested using synthetic data, which showed that the density profile could be reconstructed with an average accuracy of the order of 10 %. The method has also been applied to neutron measurements from a neutral beam heated JET discharge, which gave nd/ne ≈ 0.6 ± 0.3 in the plasma core and nd/ne ≈ 0.4 ± 0.3 towards the edge. Correction factors for detector efficiencies, neutron attenuation, and back-scattering are not yet included in the analysis; future work will aim at refining the estimated density.

Keyword
Nuclear fusion, tokamak, neutron spectrometry, neutron profile monitor, fuel ion density
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-233729 (URN)10.1063/1.4889907 (DOI)000345646000126 ()25430285 (PubMedID)
Conference
20th Topical Conference on High-Temperature Plasma Diagnostics, Atlanta, Georgia, USA, June 2014
Available from: 2014-10-09 Created: 2014-10-09 Last updated: 2017-12-05
5. Finite Larmor radii effects in fast ion measurements with neutron emission spectrometry
Open this publication in new window or tab >>Finite Larmor radii effects in fast ion measurements with neutron emission spectrometry
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2013 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, no 1, 015008- p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-192528 (URN)10.1088/0741-3335/55/1/015008 (DOI)000312586000028 ()
Conference
18th International Stellarator Hellotron Workshop and 10th Asia Pacific Plasma Theory Conference; Australian Natl Univ, Canberra, AUSTRALIA; 30 Jan-3 Feb 2012
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2017-12-06
6. Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET
Open this publication in new window or tab >>Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET
Show others...
2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 12, 123026Article in journal (Refereed) Published
Abstract [en]

Observations made in a JET experiment aimed at accelerating deuterons to the MeV range by third harmonic radio-frequency (RF) heating coupled into a deuterium beam are reported. Measurements are based on a set of advanced neutron and gamma-ray spectrometers that, for the first time, observe the plasma simultaneously along vertical and oblique lines of sight. Parameters of the fast ion energy distribution, such as the high energy cut-off of the deuteron distribution function and the RF coupling constant, are determined from data within a uniform analysis framework for neutron and gamma-ray spectroscopy based on a one-dimensional model and by a consistency check among the individual measurement techniques. A systematic difference is seen between the two lines of sight and is interpreted to originate from the sensitivity of the oblique detectors to the pitch-angle structure of the distribution around the resonance, which is not correctly portrayed within the adopted one dimensional model. A framework to calculate neutron and gamma-ray emission from a spatially resolved, two-dimensional deuteron distribution specified by energy/pitch is thus developed and used for a first comparison with predictions from ab initio models of RF heating at multiple harmonics.

The results presented in this paper are of relevance for the development of advanced diagnostic techniques for MeV range ions in high performance fusion plasmas, with applications to the experimental validation of RF heating codes and, more generally, to studies of the energy distribution of ions in the MeV range in high performance deuterium and deuterium-tritium plasmas.

Keyword
fusion, tokamak, fast ions, neutron spectrometry, gamma-ray spectroscopy
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-247990 (URN)10.1088/0029-5515/55/12/123026 (DOI)000366534500028 ()
Available from: 2015-03-25 Created: 2015-03-25 Last updated: 2017-12-04Bibliographically approved

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