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Neutron emission generated by fast deuterons accelerated with ion cyclotron heating at JET
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. (Fusion diagnostics)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
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2010 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, no 2, 022001- p.Article in journal, Letter (Refereed) Published
Abstract [en]

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 Alfvén eigenmodes.

Place, publisher, year, edition, pages
2010. Vol. 50, no 2, 022001- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-114441DOI: 10.1088/0029-5515/50/2/022001ISI: 000275322200002OAI: oai:DiVA.org:uu-114441DiVA: diva2:294065
Available from: 2010-02-16 Created: 2010-02-16 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Diagnosing Fuel Ions in Fusion Plasmas using Neutron Emission Spectroscopy
Open this publication in new window or tab >>Diagnosing Fuel Ions in Fusion Plasmas using Neutron Emission Spectroscopy
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 87 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 716
Keyword
fusion, plasma diagnostics, neutron spectroscopy, NBI heating, ICRF heating, energetic ions
National Category
Fusion, Plasma and Space Physics Subatomic Physics
Research subject
Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-114449 (URN)978-91-554-7727-1 (ISBN)
Public defence
2010-03-31, Häggsalen, Lägerhyddsvägen 1, Ångströmslaboratoriet, 10:15 (English)
Opponent
Supervisors
Available from: 2010-03-10 Created: 2010-02-16 Last updated: 2010-03-10Bibliographically approved
2. Fusion Plasma Observations at JET with the TOFOR Neutron Spectrometer: Instrumental Challenges and Physics Results
Open this publication in new window or tab >>Fusion Plasma Observations at JET with the TOFOR Neutron Spectrometer: Instrumental Challenges and Physics Results
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The neutron spectrometer TOFOR was installed at JET in 2005 for high-rate observation of neutrons from reactions between two deuterium (D) ions. Neutron spectrometry as a fusion plasma diagnostic technique is invoked to obtain information about the velocity states of fusion fuel ions. Based on neutron spectrometry data, conclusions can be drawn on the efficiency of plasma heating schemes as well as optimization of fuel ion confinement. The quality of TOFOR analysis is found to depend on how well the instrument response function is known; discriminator threshold levels, detector time alignment and electronics broadening are identified as crucial issues.

About 19 percent of the neutrons observed with TOFOR have scattered off the JET vessel wall or other structures in the line-of-sight before reaching the instrument, as established through simulations and measurements. A method has been developed to take these neutrons into account in the analysis. TOFOR measurements of fast deuterium distributions are seen to agree with distributions deduced from NPA data, obtained based on an entirely different principle. This serves as validation of the modeling and analysis.

Extraordinary statistics in the TOFOR measurements from JET pulses heated with 3rd harmonic RF heating on D beams allow for study of instabilities using neutron emission spectrometry. At ITER, similar studies should be possible on a more regular basis due to higher neutron rates.

Observations of neutrons from Be+3He reactions in the TOFOR spectrum from D plasmas heated with fundamental RF tuned to minority 3He raise the question of beryllium neutrons at JET after installation of the ITER-like wall, and at ITER, with beryllium as the plasma facing component. This is especially important for the first few years of ITER operation, where the machine will not yet have been certified as a nuclear facility and should be run in zero-activation mode.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 110 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 715
Keyword
Fusion, Plasma diagnostics, Neutron Spectrometry, TOFOR, JET, ITER, time-of-flight, plasma heating
National Category
Subatomic Physics
Research subject
Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-114077 (URN)978-91-554-7724-0 (ISBN)
Public defence
2010-03-26, Polhemsalen, Ångströmlaboratoriet, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-03-04 Created: 2010-02-09 Last updated: 2010-06-08Bibliographically approved

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Hellesen, CarlGatu Johnson, Maria

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