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Making TOFu: Fusion Plasma Neutron Emission Spectrometry with a Fully Digital Data Acquisition System
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.ORCID iD: 0000-0002-0575-1749
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

TOFu (Time-Of-Flight upgrade) is a fully digital data acquisition system based on 1 GSPS, 12 bit digitisers for the TOFOR (Time-Of-Flight spectrometer Optimised for Rate) fusion neutron spectrometer at JET. The system has been assessed, developed and subsequently tested during experimental campaigns at JET. A detailed presentation is provided, describing the electronics setup, as well as solutions to challenges related to time-alignment and synchronisation of the signal lines and digitisers.

The system enables kinematic discrimination of spectral background, based on associated time and energy measurements. This technique has been tested with synthetic data, evaluated, and compared to experimental results. The kinematic background discrimination method is shown to provide improvements in signal-to-background ratio of up to 500 % in certain spectral regions.

TOFOR is optimised for spectrometry of deuterium-deuterium fusion neutron emission at JET. The primary purpose of TOFu is to enable TOFOR to retain these spectrometric capabilities in the presence of a strong background of high-energy deuterium-tritium fusion emission neutrons, in a forthcoming deuterium-tritium fusion plasma campaign at JET. However, the improvement in signal-to-background ratio also allows for detailed studies of low-intensity spectral components, such as the contribution due to neutrons scattering off the internal wall of the JET tokamak before impinging on the TOFOR sight line. Satisfying experimental results pertaining to this aspect of spectral analysis with TOFu data are shown.

Finally, a conceptual backscattering time-of-flight spectrometer, based on deuterated scintillator detectors is presented. The backscattering time-of-flight technique is shown to be able to provide high-resolution spectrometric capabilities of deuterium-tritium fusion plasma neutron emission. Studies with synthetic data are used to demonstrate these capabilities and the effects of the developed background discrimination techniques on deuterium-tritium fusion neutron spectra obtained with the instrument.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1435
Keyword [en]
fusion, plasma diagnostics, neutron spectrometry, TOFOR, tokamak, JET, digital data acquisition
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-304383ISBN: 978-91-554-9708-8OAI: oai:DiVA.org:uu-304383DiVA: diva2:1028875
Public defence
2016-11-25, Å4001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Supervisors
Available from: 2016-11-02 Created: 2016-10-04 Last updated: 2016-11-16
List of papers
1. Fully digital data acquisition system for the neutron time-of-flight spectrometer TOFOR at JET
Open this publication in new window or tab >>Fully digital data acquisition system for the neutron time-of-flight spectrometer TOFOR at JET
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2012 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 83, no 10, 10D907- p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

A prototype of a fully digital data acquisition system based on 1 Gsps 12 bit digitizers for the TOFOR fusion neutron spectrometer at JET is assessed. The prototype system enables the use of geometry-based background discrimination techniques, which are modeled, evaluated, and compared to experimental data. The experimental results are in line with the models and show a significant improvement in signal-to-background ratio in measured time-of-flight spectrum compared to the existing data acquisition system.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-186841 (URN)10.1063/1.4734493 (DOI)000311562900095 ()
Conference
THE 19TH TOPICAL CONFERENCE ON HIGH-TEMPERATURE PLASMA DIAGNOSTICS, May 6-10, 2012, Monterey, CA, USA
Available from: 2012-12-06 Created: 2012-11-29 Last updated: 2016-10-04Bibliographically approved
2. Impact of digitization for timing and pulse shape analysis of scintillator detector signals
Open this publication in new window or tab >>Impact of digitization for timing and pulse shape analysis of scintillator detector signals
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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, Vol. 720, 135-140 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

In this paper we investigate the effects of full digitization of scintillator signals. The requirements on the analog to digital converter (ADC), in terms of sampling rate (f(s)) and bit resolution, are investigated. Two applications for scintillator detectors are studied, pulse timing and particle species identification. We find that signal reconstruction using sinc interpolation can be used e.g. for high-precision timing of a sampled electric pulse. Timing performances better than 6 ps (FWHM) were obtained if f(s) equals or exceeds twice the maximum frequency of the scintillator pulse. Failing to meet this criterion deteriorates both the performance of pulse timing and particle identification. We find that the bit resolution of the ADC is very important also for timing of pulses.

Keyword
Scintillator, Digitization, Pulse shape analysis, Pulse timing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-204253 (URN)10.1016/j.nima.2012.12.016 (DOI)000320597900035 ()
Conference
2nd International Conference on Frontiers in Diagnostic Technologies (FDT), NOV 28-30, 2011, Frascati, ITALY
Available from: 2013-07-30 Created: 2013-07-29 Last updated: 2016-10-04Bibliographically approved
3. Prospects for measuring the fuel ion ratio in burning ITER plasmas using a DT neutron emission spectrometer
Open this publication in new window or tab >>Prospects for measuring the fuel ion ratio in burning ITER plasmas using a DT neutron emission spectrometer
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2014 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 11, 11D825- p.Article in journal (Refereed) Published
Abstract [en]

The fuel ion ratio n(t)/n(d) is an essential parameter for plasma control in fusion reactor relevant applications, since maximum fusion power is attained when equal amounts of tritium (T) and deuterium (D) are present in the plasma, i.e., n(t)/n(d) = 1.0. For neutral beam heated plasmas, this parameter can be measured using a single neutron spectrometer, as has been shown for tritium concentrations up to 90%, using data obtained with the MPR (Magnetic Proton Recoil) spectrometer during a DT experimental campaign at the Joint European Torus in 1997. In this paper, we evaluate the demands that a DT spectrometer has to fulfill to be able to determine n(t)/n(d) with a relative error below 20%, as is required for such measurements at ITER. The assessment shows that a back-scattering time-of-flight design is a promising concept for spectroscopy of 14 MeV DT emission neutrons.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-240138 (URN)10.1063/1.4890577 (DOI)000345646000079 ()25430238 (PubMedID)
Available from: 2015-01-07 Created: 2015-01-05 Last updated: 2016-10-04
4. A prototype fully digital data acquisition system upgrade for the TOFOR neutron spectrometer at JET
Open this publication in new window or tab >>A prototype fully digital data acquisition system upgrade for the TOFOR neutron spectrometer at JET
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2016 (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. 833, 94-104 p.Article in journal (Refereed) Published
Abstract [en]

A prototype of a fully digital data acquisition system upgrade for the TOFOR time-of-flight fusion neutron spectrometer at JET has been implemented and evaluated. The core of the system, is composed of five fast PXle waveform digitisers (1 GSPS, 12 bits) with large internal fast memory (1 GB). Due to the complexity and high requirements on timing precision of the spectrometer, the design and implementation of such a system poses numerous technical challenges, in particular regarding time alignment and synchronisation of signal paths and digitiser modules. These issues and their solutions, as pertaining to the TOFOR spectrometer, are presented in detail in the present paper. As a final assessment of the ability of the new data acquisition system to reproduce the capabilities of the original TOFOR system, a thorough comparison of results produced using both systems is presented. The comparison with TOFOR has been performed with satisfying results. Two immediate advantages of the new data acquisition system are significantly improved triggering dead time (from about 70 ns to 10 ns) and the ability to adjust the triggering thresholds as needed during the analysis step. The enhanced spectroscopic capabilities of the new data acquisition system will be reported on in future publications.

Keyword
Fusion; Neutron spectroscopy; Time-of-flight spectroscopy; Data acquisition; JET; TOFOR
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-304367 (URN)10.1016/j.nima.2016.07.026 (DOI)000383818200016 ()
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2016-10-18Bibliographically approved
5. Kinematic Background Discrimination Methods Using a Fully Digital Data Acquisition System for TOFOR
Open this publication in new window or tab >>Kinematic Background Discrimination Methods Using a Fully Digital Data Acquisition System for TOFOR
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2016 (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. 838, 82-88 p.Article in journal (Other academic) Published
Abstract [en]

A fully digital, prototype data acquisition system upgrade for the TOFOR neutron time-of-flight neutron spectrometer at the JET experimental fusion reactor in Culham, England, has been constructed. This upgrade, TOFu (Time-of-Flight upgrade), enables digitization of associated time and energy deposition information from the TOFOR scintillator detectors, facilitating discrimination of spectral background due to unrelated neutron events based on kinematic considerations. In this publication, a kinematic background discrimination method is presented using synthetic data and validated with experimental results. It is found that an improvement in signal-to-background ratio of 500% in certain spectral regions is possible with the new DAQ system.

Keyword
Fusion; Time-of-flight spectrometry; JET; Neutron spectrometry; TOFOR; Data acquisition
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-304381 (URN)10.1016/j.nima.2016.09.030 (DOI)
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2016-12-01Bibliographically approved
6. Analysis of fusion neutron time-of-flight spectra using kinematic background discrimination
Open this publication in new window or tab >>Analysis of fusion neutron time-of-flight spectra using kinematic background discrimination
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(English)Manuscript (preprint) (Other academic)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-304382 (URN)
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2016-10-04

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