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Neutron Spectrometry Techniques for Fusion Plasmas: Instrumentation and Performance
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 726
Keywords [en]
fusion, plasma diagnostics, neutron spectrometry, neutron spectroscopy, MPRu, magnetic proton recoil spectrometer, fusion, ITER
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-121615ISBN: 978-91-554-7767-7 (print)OAI: oai:DiVA.org:uu-121615DiVA, id: diva2:305954
Public defence
2010-05-12, Häggsalen, Angstrom Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-04-20 Created: 2010-03-25 Last updated: 2011-01-12Bibliographically approved
List of papers
1. The thin-foil magnetic proton recoil neutron spectrometer MPRu at JET
Open this publication in new window or tab >>The thin-foil magnetic proton recoil neutron spectrometer MPRu at JET
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2009 (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. 610, no 3, p. 682-699Article in journal (Refereed) Published
Abstract [en]

Neutrons are produced in fusion energy experiments with both deuterium (D) and deuterium–tritium (DT) plasmas. Neutron spectroscopy is a valuable tool in the study of the underlying fuel ion populations. The magnetic proton recoil neutron spectrometer, originally installed at JET in 1996 for 14-MeV neutron measurements, has been upgraded, with the main aim of improving its signal-to-background ratio (S/B), making measurements of the 2.5-MeV neutron emission in D plasmas possible. The upgrade includes a new focal-plane detector, based on the phoswich technique and consequently less sensitive to background, and a new custom-designed digital data acquisition system based on transient recorder cards. Results from JET show that the upgraded MPRu can measure 2.5-MeV neutrons with S/B=5, an improvement by a factor of 50 compared with the original MPR. S/B of 2.8×104 in future DT experiments is estimated. The performance of the MPRu is exemplified with results from recent D plasma operations at JET, concerning both measurements with Ohmic, ion cyclotron resonance (ICRH) and neutral beam injection (NBI) plasma heating, as well as measurements of tritium burn-up neutrons. The upgraded instrument allows for 2.5-MeV neutron emission and deuterium ion temperature measurements in plasmas with low levels of tritium, a feature necessary for the ITER experiment.

Keywords
Neutron, Spectrometer, 14 MeV neutrons, 2.5 MeV neutrons, MPR, MPRu, Fusion, Diagnostic
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-129551 (URN)10.1016/j.nima.2009.09.025 (DOI)000273157600010 ()
Available from: 2010-08-19 Created: 2010-08-18 Last updated: 2017-12-12Bibliographically approved
2. Gain stabilization control system of the upgraded magnetic protonrecoil neutron spectrometer at JET
Open this publication in new window or tab >>Gain stabilization control system of the upgraded magnetic protonrecoil neutron spectrometer at JET
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2009 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 80, no 6, p. 063505-Article in journal (Refereed) Published
Abstract [en]

Burning plasma experiments such as ITER and DEMO require diagnostics capable of withstanding the harsh environment generated by the intense neutron flux and to maintain stable operating conditions for times longer than present day systems. For these reasons, advanced control and monitoring (CM) systems will be necessary for the reliable operation of diagnostics. This paper describes the CM system of the upgraded magnetic proton recoil neutron spectrometer installed at the Joint European Torus focusing in particular on a technique for the stabilization of the gain of the photomultipliers coupled to the neutron detectors. The results presented here show that this technique provides good results over long time scales. The technique is of general interest for all diagnostics that employ scintillators coupled to photomultiplier tubes.

Keywords
fusion reactor instrumentation, neutron detection, neutron flux, neutron spectrometers, photomultipliers, plasma diagnostics, plasma toroidal confinement, scintillation counters, Tokamak devices
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-121514 (URN)10.1063/1.3109682 (DOI)000267600600016 ()
Available from: 2010-03-24 Created: 2010-03-24 Last updated: 2017-12-12Bibliographically approved
3. Neutron emission spectroscopy diagnosis of JET D and DT plasmas with the new MPRu instrument
Open this publication in new window or tab >>Neutron emission spectroscopy diagnosis of JET D and DT plasmas with the new MPRu instrument
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2006 (English)In: 33rd EPS Conference on Plasma Phys. and Contr. Fusion, 2006, p. 30I P-1.071Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:uu:diva-24830 (URN)
Available from: 2007-02-07 Created: 2007-02-07 Last updated: 2017-01-25
4. Evaluation of Spectral Unfolding for Neutron Spectroscopy
Open this publication in new window or tab >>Evaluation of Spectral Unfolding for Neutron Spectroscopy
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2007 (English)Report (Other (popular scientific, debate etc.))
Identifiers
urn:nbn:se:uu:diva-13737 (URN)
Note
and JET EFDA contributors (EFD -C(07)04/10)Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2017-01-25
5. Instrumentation for neutron emission spectrometry in use at JET
Open this publication in new window or tab >>Instrumentation for neutron emission spectrometry in use at JET
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2010 (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. 623, no 2, p. 681-685Article in journal (Refereed) Published
Abstract [en]

The present contribution discusses two neutron spectrometers: the time-of-flight spectrometer (TOFOR) and the magnetic proton recoil spectrometer (MPRu). TOFOR uses fast plastic scintillators equipped with digital time-stamping electronics to register the time of each eligible scintillation event. The time trace for each detector is acquired practically dead-time free. The detectors of the MPRu are of phoswich type and each detector is connected to a digital transient recorder card that stores the full waveform for an event. By using phoswich detectors, pulse-shape discrimination techniques can be applied offline to distinguish signal events from background. A future upgrade of TOFOR could be digital “hybrid” cards, which store correlated time and waveform information. This information can be used to decrease the background level in the ttof spectrum, thereby increasing the operating range.

Keywords
Fusion diagnostic, Neutron emission spectrometry, MPRu, TOFOR, Data acquisition systems
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-121517 (URN)10.1016/j.nima.2010.02.255 (DOI)000284343600010 ()
Available from: 2010-03-24 Created: 2010-03-24 Last updated: 2017-12-12Bibliographically approved
6. Evaluation of neutron spectrometer techniques for ITER using synthetic data
Open this publication in new window or tab >>Evaluation of neutron spectrometer techniques for ITER using synthetic data
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2013 (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. 701, p. 17p. 62-71Article in journal (Refereed) Published
Abstract [en]

A neutron spectrometer at ITER is expected to provide estimates of plasma parameters such as ion temperature, Ti, fuel ion ratio, nt/nd, and Qthermal/Qtot, with 10-20% precision at a time resolution, Δt, of at least 100 ms. The present paper describes a method for evaluating different neutron spectroscopy techniques based on their instrumental response functions and synthetic measurement data. We include five different neutron spectrometric techniques with realistic response functions, based on simulations and measurements where available. The techniques are magnetic proton recoil, thin-foil proton recoil, gamma discriminating organic scintillator, diamond and time-of-flight. The reference position and line of sight of a high resolution neutron spectrometer on ITER are used in the study. ITER plasma conditions are simulated for realistic operating scenarios. The ITER conditions evaluated are beam and radio frequency heated and thermal deuterium-tritium plasmas. Results are given for each technique in terms of the estimated time resolution at which the parameter determination can be made within the required precision (here 10% for Ti and the relative intensities of NB and RF emission components). It is shown that under the assumptions made, the thin-foil techniques out-perform the other spectroscopy techniques in practically all measurement situations. For thermal conditions, the range of achieved Δt in the determination of Ti varies in time scales from ms (for the magnetic and thin-foil proton recoil) to s (for gamma discriminating organic scintillator).

Publisher
p. 17
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-121519 (URN)10.1016/j.nima.2012.10.041 (DOI)000313721400010 ()
Available from: 2010-04-12 Created: 2010-03-24 Last updated: 2017-12-12Bibliographically approved

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