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Neutron emission spectroscopy of fusion plasmas with a NE213 liquid scintillator at JET
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. (Nuclear Fusion)
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Neutron diagnostics will play a fundamental role in future fusion plasma machines,where the harsh environment will make the use of many other type of diagnos-tics practically impossible. Complex techniques to measure the neutron spectrumemitted from tokamk plasmas have been developed over the years, producing stateof the art neutron spectrometers. However, recently compact neutron spectrom-eters have been gaining the interest of the research community. They are muchsimpler to operate and maintain, have lower cost and they can be employed in thechannels of a neutron camera, providing profile measurements. The drawbacks arethat they have a worse resolution and a response to neutrons that is not optimalfor spectroscopy.The goal of the work presented in this thesis is to estimate to which extenta compact detector such as a NE213 liquid scintillator can be used to performneutron emission spectroscopy analysis.The detector used for this study was installed in the back of the MPRu spec-trometer at JET in 2012. The characterization of the response of the detector wasdone using a combination of MCNPX simulations and real measurements. Thedata analysis was performed using the forward fitting approach: a model of theneutron spectrum is produced, then folded with the response of the detector andfinally compared with the data. Two types of plasma scenarios were analyzed, onewith NBI heating only, and another with NBI and third harmonic radio-frequencyheating. In both cases the TOFOR spectrometer was used as a reference to esti-mate the parameters in the model of the neutron spectrum.The results are promising and suggest that neutron spectroscopy can be per-formed with NE213 scintillators although the quality of the results, as given byperformance indicators such as uncertainties, is much lower than the performanceof high resolution spectrometers.

Place, publisher, year, edition, pages
Uppsala: Uppsala University , 2015.
Keyword [en]
NE213, neutron spectroscopy, liquid scintillator, nuclear, fusion, plasma
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:uu:diva-291506OAI: oai:DiVA.org:uu-291506DiVA: diva2:925705
Presentation
2015-05-18, 15:15 (English)
Opponent
Supervisors
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2016-05-09Bibliographically approved
List of papers
1. Monte Carlo Simulation Of The Data Acquisition Chain Of Scintillation Detectors
Open this publication in new window or tab >>Monte Carlo Simulation Of The Data Acquisition Chain Of Scintillation Detectors
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2014 (English)In: International Conference on Fusion Reactor Diagnostics, SEP 09-13, 2013, Varenna, ITALY, 2014, 101-104 p.Conference paper, Published paper (Refereed)
Abstract [en]

The good performance of a detector can be strongly affected by the instrumentation used to acquire the data. The possibility of anticipating how the acquisition chain will affect the signal can help in finding the best solution among different set-ups. In this work we developed a Monte Carlo code that aims to simulate the effect of the various components of a digital Data Acquisition system (DAQ) applied to scintillation detectors. The components included in the model are: the scintillator, the photomultiplier tube (PMT), the signal cable and the digitizer. We benchmarked the code against real data acquired with a NE213 scintillator, comparing simulated and real signal pulses induced by gamma-ray interaction. Then we studied the dependence of the energy resolution of a pulse height spectrum (PHS) on the sampling frequency and the bit resolution of the digitizer. We found that exceeding some values of the sampling frequency and the bit resolution improves only marginally the performance of the system. The method can be applied for the study of various detector systems relevant for nuclear techniques, such as in fusion diagnostics.

Series
AIP Conference Proceedings, ISSN 0094-243X ; 1612
Keyword
Data acquisition, Scintillators, Photomultiplier tubes, Digitizers, NE213, Gamma-rays, Resolution, Monte Carlo
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-237652 (URN)10.1063/1.4894032 (DOI)000343712300017 ()978-0-7354-1248-4 (ISBN)
Conference
International Conference on Fusion Reactor Diagnostics, SEP 09-13, 2013, Varenna, ITALY
Available from: 2014-12-11 Created: 2014-12-03 Last updated: 2016-05-03Bibliographically approved
2. Forward fitting of experimental data from a NE213 neutron detector installed with the magnetic proton recoil upgraded spectrometer at JET
Open this publication in new window or tab >>Forward fitting of experimental data from a NE213 neutron detector installed with the magnetic proton recoil upgraded spectrometer at JET
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2014 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 11, 11E123- p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we present the results obtained from the data analysis of neutron spectra measured with a NE213 liquid scintillator at JET. We calculated the neutron response matrix of the instrument combining MCNPX simulations, a generic proton light output function measured with another detector and the fit of data from ohmic pulses. For the analysis, we selected a set of pulses with neutral beam injection heating (NBI) only and we applied a forward fitting procedure of modeled spectral components to extract the fraction of thermal neutron emission. The results showed the same trend of the ones obtained with the dedicated spectrometer TOFOR, even though the values from the NE213 analysis were systematically higher. This discrepancy is probably due to the different lines of sight of the two spectrometers (tangential for the NE213, vertical for TOFOR). The uncertainties on the thermal fraction estimates were from 4 to 7 times higher than the ones from the TOFOR analysis.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-240136 (URN)10.1063/1.4895565 (DOI)000345646000143 ()25430302 (PubMedID)
Available from: 2015-01-07 Created: 2015-01-05 Last updated: 2017-12-05
3. Analysis of the fast ion tails observed in the NE213pulse height specta measured during third harmonicradio-frequency heating experiments at JET
Open this publication in new window or tab >>Analysis of the fast ion tails observed in the NE213pulse height specta measured during third harmonicradio-frequency heating experiments at JET
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this paper we investigate the possibility of using a NE213 liquid scintillator as aneutron spectrometer to diagnose the fast ion tails produced in experiments with 3rd harmonicradio-frequency heating.We discuss mainly the instrumental effects that need to be considered and corrected for in orderto obtain a good agreement between measured data and models: gain drift, pile-up, impact of theassumption of a standard proton light yield function. We also address problems related to thepresence of triton burn-up events in the spectrum.The expected ion distribution is obtained from a simple 1D Fokker-Planck model. The parametersof the model are estimated using the data collected by the TOFOR neutron spectrometer.The agreement between the data and the model is good and it is possible to make a clear distinctionbetween discharges that had different electron densities and thus different cut-off energies. Wecan conclude that NE213 scintillators can provide useful spectroscopic information for this kind ofexperiments.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-292741 (URN)
Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2016-07-18Bibliographically approved

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