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Modelling and Measurements of MAST Neutron Emission
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Measurements of neutron emission from a fusion plasma can provide a wealth of information on the underlying temporal, spatial and energy distributions of reacting ions and how they are affected by a wide range of magneto-hydro-dynamic (MHD) instabilities.

This thesis focuses on the interpretation of the experimental measurements recorded by neutron flux monitors with and without spectroscopic capabilities installed on the Mega Ampere Spherical Tokamak (MAST). In particular, the temporally and spatially resolved measurements of the neutron rate measured by the neutron camera, which also possesses spectroscopic capabilities, are combined with the temporally resolved measurements of the total neutron rate provided by the absolutely calibrated fission chamber in order to study the properties of the fast ion distributions in different plasma scenarios.

The first part of the thesis describes in detail the two forward modelling methods, which employ the set of interconnected codes developed to interpret experimental observations such as neutron count rate profiles and recoil proton pulse height spectra provided by the neutron camera. In the second part of the thesis the developed methods are applied to model the neutron camera observations performed in a variety of plasma scenarios. The first method, which involves only TRANSP/NUBEAM and LINE2 codes, was used to validate the neutron count rate profiles measured by the neutron camera in three different plasma scenarios covering the wide range of total neutron rate typically observed on MAST. In addition, the first framework was applied to model the changes in the total and local neutron rates caused by fishbone instability as well as to estimate the Hydrogen and Deuterium ion ratio. The second modelling method, which involves TRANSP/NUBEAM, LINE2, DRESS and NRESP, was used to validate the measured recoil proton pulse height spectra in a MHD-quiescent plasma scenario.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1364
Keyword [en]
fusion, plasma diagnostics, neutron emissivity and rate, Neutron Camera, tokamak, MAST
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-282122ISBN: 978-91-554-9541-1 (print)OAI: oai:DiVA.org:uu-282122DiVA: diva2:916806
Public defence
2016-05-26, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-05-04 Created: 2016-04-02 Last updated: 2016-05-12
List of papers
1. TRANSP modelling of neutron emissivity on MAST
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2012 (English)Conference proceedings (editor) (Other academic)
Abstract [en]

The aim of this paper is to validate a set of methods to model the measured neutron emission on Mega Amp Spherical Tokamak (MAST) using TRANSP. Neutrons are measured along a set of collimated lines of sight (LoS) at MAST by a Neutron Camera (NC). The neutron emissivity is modeled with TRANSP [1] for different plasma discharges using a selfconsistent data set produced by a data preparation and analysis tool. The modeled neutron emissivity is then compared with NC experimental data using a full 3D solid angle calculation to model the transport of neutrons from plasma to detector. A good agreement between the modelled and experimental neutron rate was found.

Place, publisher, year, edition, pages
010 Publishers, 2012
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-275195 (URN)
Conference
39th EPS Conference & 16th Int. Congress on Plasma Physics, Stockholm, 2-6 July, 2012
Available from: 2016-02-01 Created: 2016-02-01 Last updated: 2016-05-12
2. TRANSP modelling of total and local neutron emission on MAST
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2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 2, 023003Article in journal (Refereed) Published
Abstract [en]

The results of TRANSP simulations of neutron count rate profiles measured by a collimated neutron flux monitor-neutron camera (NC)-for different plasma scenarios on MAST are reported. In addition, the effect of various plasma parameters on neutron emission is studied by means of TRANSP simulation. The fast ion redistribution and losses due to fishbone modes, which belong to a wider category of energetic particle modes, are observed by the NC and modelled in TRANSP.

Keyword
neutron measurements, TRANSP/NUBEAM simulations, fishbone
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-247139 (URN)10.1088/0029-5515/55/2/023003 (DOI)000348843100004 ()
Available from: 2015-03-17 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved
3. TRANSP modelling of experimentally measured fast particle redistribution and losses on MAST
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2013 (English)Conference proceedings (editor) (Other academic)
Abstract [en]

MAST is a mid-size spherical tokamak with BT = 0.3-0.6 T and two NBI systems delivering up to 3.5 MW of super-Alfvénic deuterons and therefore suitable for understanding the dynamics of fast particles in ITER-relevant scenarios. It is well known that MHD instabilities can cause redistribution and/or losses of fast ions as observed in many tokamaks (such as NSTX, TFTR, DIII-D, JET, ASDEX, NSTX and MAST). In particular, on MAST, the effect of fast particle driven instabilities, such as fishbones and long-lived modes upon the total neutron yield measured by fission chamber (FC) and the neutron count rates measured by Neutron Camera (NC) has been observed [1]. Fishbones are characterized by burst-like behaviour observed in magnetic and SXR diagnostics and by the sweeping of the mode frequency during a burst. The resonant interaction between the toroidal and poloidal motion of the fast ions in the plasma with the n = 1, m = 1 internal kink mode is the mechanism responsible for driving the fishbone instability [2].

Place, publisher, year, edition, pages
010 Publishers, 2013
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-275193 (URN)
Conference
40th EPS Conference on Plasma Physics, Espoo, Finland, 1-5 July, 2013
Available from: 2016-02-01 Created: 2016-02-01 Last updated: 2016-05-12
4. Determination of hydrogen/deuterium ratio with neutron measurements on MAST
Open this publication in new window or tab >>Determination of hydrogen/deuterium ratio with neutron measurements on MAST
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2014 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 11, 11E109- p.Article in journal (Refereed) Published
Abstract [en]

On MAST, compressional Alfven eigenmodes can be destabilized by the presence of a sufficiently large population of energetic particles in the plasma. This dependence was studied in a series of very similar discharges in which increasing amounts of hydrogen were puffed into a deuterium plasma. A simple method to estimate the isotopic ratio n(H)/n(D) using neutron emission measurements is here described. The inferred isotopic ratio ranged from 0.0 to 0.6 and no experimental indication of changes in radial profile of n(H)/n(D) were observed. These findings are confirmed by TRANSP/NUBEAM simulations of the neutron emission.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-240140 (URN)10.1063/1.4889910 (DOI)000345646000129 ()25430288 (PubMedID)
Available from: 2015-01-07 Created: 2015-01-05 Last updated: 2017-12-05Bibliographically approved
5. Validation of neutron emission and neutron energy spectrum calculations on MAST with DRESS
Open this publication in new window or tab >>Validation of neutron emission and neutron energy spectrum calculations on MAST with DRESS
(English)Article in journal (Refereed) Submitted
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-281186 (URN)
Available from: 2016-03-20 Created: 2016-03-20 Last updated: 2016-05-12

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