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The 2.5-MeV neutron time-of-flight spectrometer TOFOR for experiments at JET
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.
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, Technology, Department of Engineering Sciences, Electricity.
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2008 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 591, no 2, 417-430 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 591, no 2, 417-430 p.
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-16750DOI: 10.1016/j.nima.2008.03.010ISI: 000257529700011OAI: oai:DiVA.org:uu-16750DiVA: diva2:44521
Note

Conference Information: 21st IAEA Fusion Energy Conference Chengdu, PEOPLES R CHINA, OCT 16-21, 2006

Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2017-12-08Bibliographically approved
In thesis
1. 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
2. Development of Neutron Emission Spectroscopy Instrumentation for Deuterium and Deuterium-Tritium Fusion Plasmas at JET
Open this publication in new window or tab >>Development of Neutron Emission Spectroscopy Instrumentation for Deuterium and Deuterium-Tritium Fusion Plasmas at JET
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study of high power fusion plasmas at the JET tokamak has been further enhanced through the development of instrumentation for neutron emission spectroscopy (NES) measurements. This has involved the upgrade of the magnetic proton recoil (MPR) spectrometer used for deuterium-tritium plasmas earlier so that the MPRu can now be also employed for deuterium (D) plasmas. A neutron time-of-flight (TOF) spectrometer designed for optimized rate (TOFOR) has been constructed and put into operation. The MPRu and TOFOR spectrometers were carried out as part of the JET enhanced performance program and represent the most advanced instrumentation for NES diagnosis of both D and DT tokamak plasmas setting a central platform for R&D direct to the next step in fusion research to be carried out with ITER.

The MPRu work presented in this thesis concerns the development of a new focal plane detector based on the phoswich scintillator technique. The main objective of this sub-project was to increase the signal-to-background ratio to permit measurement of the 2.5-MeV neutron emission from d+d-->3He+n reactions and, hence, allow NES diagnosis of D plasmas. The objective was achieved as demonstrated in preliminary measurements at JET.

The development of TOFOR from concept to construction is presented in the thesis including, in particular, the commissioning of the instrument at JET. The objective of the TOFOR project was to achieve the same high performance in the NES diagnosis of D plasmas as had earlier been demonstrated by the MPR for DT plasmas. TOFOR has been used in the first plasma physics experiments reported in this thesis. These demonstrate that the performance objectives have been achieved as tested, in particular, in the observation of auxiliary heating effects on velocity distribution of the deuterium population.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 339
Keyword
Nuclear physics, neutron spectroscopy, MPRu, TOFOR, JET, Radio frequency heating, Count rate, Kärnfysik
Identifiers
urn:nbn:se:uu:diva-8199 (URN)978-91-554-6961-0 (ISBN)
Public defence
2007-10-05, 80101, Ångströmlab, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-09-13 Created: 2007-09-13 Last updated: 2014-01-28Bibliographically approved

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Gatu Johnson, MariaGiacomelli, LHjalmarsson, AndersKällne, JanWeiszflog, MatthiasAndersson Sundén, ErikConroy, SeanEricsson, GöranHellesen, CarlRonchi, EmanueleSjöstrand, Henrik

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Gatu Johnson, MariaGiacomelli, LHjalmarsson, AndersKällne, JanWeiszflog, MatthiasAndersson Sundén, ErikConroy, SeanEricsson, GöranHellesen, CarlRonchi, EmanueleSjöstrand, Henrik
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