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Conroy, Sean
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Publications (10 of 155) Show all publications
Cufar, A., Batistoni, P., Conroy, S., Ghani, Z., Lengar, I., Milocco, A., . . . Snoj, L. (2017). Calculations to support JET neutron yield calibration: Modelling of neutron emission from a compact DT neutron generator. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 847, 199-204.
Open this publication in new window or tab >>Calculations to support JET neutron yield calibration: Modelling of neutron emission from a compact DT neutron generator
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2017 (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. 847, 199-204 p.Article in journal (Refereed) Published
Abstract [en]

At the Joint European Torus (JET) the ex-vessel fission chambers and in-vessel activation detectors are used as the neutron production rate and neutron yield monitors respectively. In order to ensure that these detectors produce accurate measurements they need to be experimentally calibrated. A new calibration of neutron detectors to 14 MeV neutrons, resulting from deuterium tritium (DT) plasmas, is planned at JET using a compact accelerator based neutron generator (NG) in which a D/T beam impinges on a solid target containing T/D, producing neutrons by DT fusion reactions. This paper presents the analysis that was performed to model the neutron source characteristics in terms of energy spectrum, angle energy distribution and the effect of the neutron generator geometry. Different codes capable of simulating the accelerator based DT neutron sources are compared and sensitivities to uncertainties in the generator's internal structure analysed. The analysis was performed to support preparation to the experimental measurements performed to characterize the NG as a calibration source. Further extensive neutronics analyses, performed with this model of the NG, will be needed to support the neutron calibration experiments and take into account various differences between the calibration experiment and experiments using the plasma as a source of neutrons.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
Keyword
Compact DT neutron generator, MCNP, Modelling
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-320412 (URN)10.1016/j.nima.2016.12.009 (DOI)000394396800027 ()
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-04-19Bibliographically approved
Binda, F., Eriksson, J., Ericsson, G., Hellesen, C., Conroy, S., Nocente, M. & Andersson Sundén, E. (2017). Generation of the neutron response function of an NE213 scintillator for fusion applications. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 866, 222-229.
Open this publication in new window or tab >>Generation of the neutron response function of an NE213 scintillator for fusion applications
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2017 (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. 866, 222-229 p.Article in journal (Refereed) Published
Abstract [en]

In this work we present a method to evaluate the neutron response function of an NE213 liquid scintillator. This method is particularly useful when the proton light yield function of the detector has not been measured, since it is based on a proton light yield function taken from literature, MCNPX simulations, measurements of gammarays from a calibration source and measurements of neutrons from fusion experiments with ohmic plasmas. The inclusion of the latter improves the description of the proton light yield function in the energy range of interest (around 2.46 MeV). We apply this method to an NE213 detector installed at JET, inside the radiation shielding of the magnetic proton recoil (MPRu) spectrometer, and present the results from the calibration along with some examples of application of the response function to perform neutron emission spectroscopy (NES) of fusion plasmas. We also investigate how the choice of the proton light yield function affects the NES analysis, finding that the result does not change significantly. This points to the fact that the method for the evaluation of the neutron response function is robust and gives reliable results.

Keyword
NE213 scintillator, Neutron spectroscopy, Response function, Proton light yield
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-330537 (URN)10.1016/j.nima.2017.04.023 (DOI)000407863700029 ()
Available from: 2017-10-04 Created: 2017-10-04 Last updated: 2017-11-16Bibliographically approved
Weisen, H., Kim, H.-T., Strachan, J., Scott, S., Baranov, Y., Buchanan, J., . . . Santala, M. (2017). The 'neutron deficit' in the JET tokamak. Nuclear Fusion, 57(7), Article ID 076029.
Open this publication in new window or tab >>The 'neutron deficit' in the JET tokamak
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2017 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 7, 076029Article in journal (Refereed) Published
Abstract [en]

The measured D-D neutron rate of neutral beam heated JET baseline and hybrid H-modes in deuterium is found to be between approximately 50% and 100% of the neutron rate expected from the TRANSP code, depending on the plasma parameters. A number of candidate explanations for the shortfall, such as fuel dilution, errors in beam penetration and effectively available beam power have been excluded. As the neutron rate in JET is dominated by beamplasma interactions, the ` neutron deficit' may be caused by a yet unidentified form of fast particle redistribution. Modelling, which assumes fast particle transport to be responsible for the deficit, indicates that such redistribution would have to happen at time scales faster than both the slowing down time and the energy confinement time. Sawteeth and edge localised modes are found to make no significant contribution to the deficit. There is also no obvious correlation with magnetohydrodynamic activity measured using magnetic probes at the tokamak vessel walls. Modelling of fast particle orbits in the 3D fields of neoclassical tearing modes shows that realistically sized islands can only contribute a few percent to the deficit. In view of these results it appears unlikely that the neutron deficit results from a single physical process in the plasma.

Keyword
neutron yield, fusion reactions, Monte Carlo orbit code, TRANSP
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-327364 (URN)10.1088/1741-4326/aa6dcc (DOI)000402878400004 ()
Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2017-08-21Bibliographically approved
Eriksson, J., Conroy, S., Andersson Sundén, E. & Hellesen, C. (2016). Calculating fusion neutron energy spectra from arbitrary reactant distributions. Computer Physics Communications, 199, 40-46.
Open this publication in new window or tab >>Calculating fusion neutron energy spectra from arbitrary reactant distributions
2016 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 199, 40-46 p.Article in journal (Refereed) Published
Abstract [en]

The Directional Relativistic Spectrum Simulator (DRESS) code can perform Monte-Carlo calculations of reaction product spectra from arbitrary reactant distributions, using fully relativistic kinematics. The code is set up to calculate energy spectra from neutrons and alpha particles produced in the D(d, n)3He and T(d, n)4He fusion reactions, but any two-body reaction can be simulated by including the corresponding cross section. The code has been thoroughly tested. The kinematics calculations have been benchmarked against the kinematics module of the ROOT Data Analysis Framework. Calculated neutron energy spectra have been validated against tabulated fusion reactivities and against an exact analytical expression for the thermonuclear fusion neutron spectrum, with good agreement. The DRESS code will be used as the core of a detailed synthetic diagnostic framework for neutron measurements at the JET and MAST tokamaks.

Keyword
neutron energy spectra, relativistic kinematics
National Category
Fusion, Plasma and Space Physics Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-247991 (URN)10.1016/j.cpc.2015.10.010 (DOI)000367113200006 ()
Available from: 2015-03-25 Created: 2015-03-25 Last updated: 2017-12-04Bibliographically approved
Skiba, M., Ericsson, G., Hjalmarsson, A., Hellesen, C., Conroy, S., Andersson Sundén, E. & Eriksson, J. (2016). Kinematic Background Discrimination Methods Using a Fully Digital Data Acquisition System for TOFOR. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 838, 82-88.
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)000386061200013 ()
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2017-11-30Bibliographically approved
Sjöstrand, H., Conroy, S., Helgesson, P., J. Koning, A., Hernandez Solis, A., Pomp, S. & Rochman, D. (2016). Propagation Of Nuclear Data Uncertainties For Fusion Power Measurements. In: : . Paper presented at ND2016, International Conference on Nuclear Data for Science and Technology, 11-16/9 Bruges. .
Open this publication in new window or tab >>Propagation Of Nuclear Data Uncertainties For Fusion Power Measurements
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2016 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Fusion plasmas produce neutrons and by measuring the neutron emission the fusion power can be inferred. Accurate neutron yield measurements are paramount for the safe and efficient operation of fusion experiments and, eventually, fusion power plants.

Neutron measurements are an essential part of the diagnostic system at large fusion machines such as JET and ITER. At JET, a system of activation foils provides the absolute calibration for the neutron yield determination.  The activation system uses the property of certain nuclei to emit radiation after being excited by neutron reactions. A sample of suitable nuclei is placed in the neutron flux close to the plasma and after irradiation the induced radiation is measured.  Knowing the neutron activation cross section one can calculate the time-integrated neutron flux at the sample position. To relate the local flux to the total neutron yield, the spatial flux response has to be identified. This describes how the local neutron emission affects the flux at the detector.  The required spatial flux response is commonly determined using neutron transport codes, e.g., MCNP.

Nuclear data is used as input both in the calculation of the spatial flux response and when the flux at the irradiation site is inferred. Consequently, high quality nuclear data is essential for the proper determination of the neutron yield and fusion power.  However, uncertainties due to nuclear data are generally not fully taken into account in today’s uncertainty analysis for neutron yield calibrations using activation foils.  

In this paper, the neutron yield uncertainty due to nuclear data is investigated using the so-called Total Monte Carlo Method. The work is performed using a detailed MCNP model of JET fusion machine.  In this work the uncertainties due to the cross sections and angular distributions in JET structural materials, as well as the activation cross sections, are analyzed. It is shown that a significant contribution to the neutron yield uncertainty can come from uncertainties in the nuclear data.

National Category
Physical Sciences Fusion, Plasma and Space Physics Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-313491 (URN)
Conference
ND2016, International Conference on Nuclear Data for Science and Technology, 11-16/9 Bruges
Funder
EU, Horizon 2020
Available from: 2017-01-20 Created: 2017-01-20 Last updated: 2017-01-20Bibliographically approved
Bykov, I., Bergsåker, H., Possnert, G., Zhou, Y., Heinola, K., Pettersson, J., . . . Widdowson, A. (2016). Studies of Be migration in the JET tokamak using AMS with Be-10 marker. In: : . Paper presented at 22nd International Conference on Ion Beam Analysis (IBA), JUN 14-19, 2015, Opatija, CROATIA (pp. 370-375). , 371.
Open this publication in new window or tab >>Studies of Be migration in the JET tokamak using AMS with Be-10 marker
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2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The JET tokamak is operated with beryllium limiter tiles in the main chamber and tungsten coated carbon fiber composite tiles and solid W tiles in the divertor. One important issue is how wall materials are migrating during plasma operation. To study beryllium redistribution in the main chamber and in the divertor, a Be-10 enriched limiter tile was installed prior to plasma operations in 2011-2012. Methods to take surface samples have been developed, an abrasive method for bulk Be tiles in the main chamber, which permits reuse of the tiles, and leaching with hot HCl to remove all Be deposited at W coated surfaces in the divertor. Quantitative analysis of the total amount of Be in cm(2) sized samples was made with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The Be-10/Be-9 ratio in the samples was measured with accelerator mass spectrometry (AMS). The experimental setup and methods are described in detail, including sample preparation, measures to eliminate contributions in AMS from the B-10 isobar, possible activation due to plasma generated neutrons and effects of diffusive isotope mixing. For the first time marker concentrations are measured in the divertor deposits. They are in the range 0.4-1.2% of the source concentration, with moderate poloidal variation.

Keyword
Nuclear fusion, ITER-like Wall, Materials migration, Beryllium, Accelerator mass spectrometry (AMS)
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-295580 (URN)10.1016/j.nimb.2015.12.007 (DOI)000373412000074 ()
Conference
22nd International Conference on Ion Beam Analysis (IBA), JUN 14-19, 2015, Opatija, CROATIA
Available from: 2016-06-22 Created: 2016-06-08 Last updated: 2016-07-15Bibliographically approved
Batistoni, P., Conroy, S., Lilley, S., Naish, J., Obryk, B., Popovichev, S., . . . Vasilopoulou, T. (2015). Benchmark experiments on neutron streaming through JET Torus Hall penetrations. Nuclear Fusion, 55(5), Article ID 053028.
Open this publication in new window or tab >>Benchmark experiments on neutron streaming through JET Torus Hall penetrations
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2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 5, 053028Article in journal (Refereed) Published
Abstract [en]

Neutronics experiments are performed at JET for validating in a real fusion environment the neutronics codes and nuclear data applied in ITER nuclear analyses. In particular, the neutron fluence through the penetrations of the JET torus hall is measured and compared with calculations to assess the capability of state-of-art numerical tools to correctly predict the radiation streaming in the ITER biological shield penetrations up to large distances from the neutron source, in large and complex geometries. Neutron streaming experiments started in 2012 when several hundreds of very sensitive thermo-luminescence detectors (TLDs), enriched to different levels in (LiF)-Li-6/(LiF)-Li-7, were used to measure the neutron and gamma dose separately. Lessons learnt from this first experiment led to significant improvements in the experimental arrangements to reduce the effects due to directional neutron source and self-shielding of TLDs. Here we report the results of measurements performed during the 2013-2014 JET campaign. Data from new positions, at further locations in the South West labyrinth and down to the Torus Hall basement through the air duct chimney, were obtained up to about a 40m distance from the plasma neutron source. In order to avoid interference between TLDs due to self-shielding effects, only TLDs containing natural Lithium and 99.97% Li-7 were used. All TLDs were located in the centre of large polyethylene (PE) moderators, with Li-nat and Li-7 crystals evenly arranged within two PE containers, one in horizontal and the other in vertical orientation, to investigate the shadowing effect in the directional neutron field. All TLDs were calibrated in the quantities of air kerma and neutron fluence. This improved experimental arrangement led to reduced statistical spread in the experimental data. The Monte Carlo N-Particle (MCNP) code was used to calculate the air kerma due to neutrons and the neutron fluence at detector positions, using a JET model validated up to the magnetic limbs. JET biological shield and penetrations, the PE moderators and TLDs were modelled in detail. Different tallying methods were used in the calculations, which are routinely used in ITER nuclear analyses: the mesh tally and the track length estimator with multiple steps calculations using the surface source write/read capability available in MCNP. In both cases, the calculated neutron fluence (C) was compared to the measured fluence (E) and hence C/E comparisons have been obtained and are discussed. These results provide a validation of neutronics numerical tools, codes and nuclear data, used for ITER design.

Keyword
JET neutron yield, fusion neutronics, benchmark experiment
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-255276 (URN)10.1088/0029-5515/55/5/053028 (DOI)000353546700029 ()
Available from: 2015-06-22 Created: 2015-06-15 Last updated: 2017-12-04Bibliographically approved
Eriksson, J., Nocente, M., Binda, F., Cazzaniga, C., Conroy, S., Ericsson, G., . . . Weiszflog, M. (2015). Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET. Nuclear Fusion, 55(12), Article ID 123026.
Open this publication in new window or tab >>Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET
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2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 12, 123026Article in journal (Refereed) Published
Abstract [en]

Observations made in a JET experiment aimed at accelerating deuterons to the MeV range by third harmonic radio-frequency (RF) heating coupled into a deuterium beam are reported. Measurements are based on a set of advanced neutron and gamma-ray spectrometers that, for the first time, observe the plasma simultaneously along vertical and oblique lines of sight. Parameters of the fast ion energy distribution, such as the high energy cut-off of the deuteron distribution function and the RF coupling constant, are determined from data within a uniform analysis framework for neutron and gamma-ray spectroscopy based on a one-dimensional model and by a consistency check among the individual measurement techniques. A systematic difference is seen between the two lines of sight and is interpreted to originate from the sensitivity of the oblique detectors to the pitch-angle structure of the distribution around the resonance, which is not correctly portrayed within the adopted one dimensional model. A framework to calculate neutron and gamma-ray emission from a spatially resolved, two-dimensional deuteron distribution specified by energy/pitch is thus developed and used for a first comparison with predictions from ab initio models of RF heating at multiple harmonics.

The results presented in this paper are of relevance for the development of advanced diagnostic techniques for MeV range ions in high performance fusion plasmas, with applications to the experimental validation of RF heating codes and, more generally, to studies of the energy distribution of ions in the MeV range in high performance deuterium and deuterium-tritium plasmas.

Keyword
fusion, tokamak, fast ions, neutron spectrometry, gamma-ray spectroscopy
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-247990 (URN)10.1088/0029-5515/55/12/123026 (DOI)000366534500028 ()
Available from: 2015-03-25 Created: 2015-03-25 Last updated: 2017-12-04Bibliographically approved
Koskela, T., Romanelli, M., Belo, P., Asunta, O., Sipilae, S., O'Mullane, M., . . . Kurki-Suonio, T. (2015). Effect of tungsten off-axis accumulation on neutral beam deposition in JET rotating plasmas. Plasma Physics and Controlled Fusion, 57(4), Article ID 045001.
Open this publication in new window or tab >>Effect of tungsten off-axis accumulation on neutral beam deposition in JET rotating plasmas
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2015 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 4, 045001Article in journal (Refereed) Published
Abstract [en]

Evidence for low field side accumulation of tungsten is often observed in bolometry and soft x-ray emissivities of highly rotating JET ITER-like wall (ILW) plasmas. Poloidal variation of the density of high-Z impurities, such as tungsten, in the core of NBI heated plasmas is expected from neoclassical theory due to charge displacement and parallel electric field generated by the centrifugal force. We calculate the poloidally asymmetric distribution of tungsten using fluid equations and a 1D transport simulation with the JETTO/SANCO code. Peaking of tungsten on the outboard side of the plasma is found and verified with soft x-ray and bolometry measurements. We then study the effect of a poloidally asymmetric tungsten distribution on the distribution of the NBI heat source by simulations with the Monte Carlo code ASCOT. The simulations show that the poloidally asymmetric tungsten profile redistributes the fast NBI ions radially through shifting their ionization profile and poloidally through enhanced pitch-angle scattering at high energy. The amplitude of the redistribution is in the order of 10% for the highest n(W)/n(e) ratios of similar to 10(-4) measured in recent JET H-mode plasmas. As a result of the scattering of the beam particles, the core heat deposition is changed less than 10%, which does not have a significant impact to the performance of JET plasmas. The modelling is in qualitative agreement with measurements by the vertical neutron camera that sees a broadening in the 2.5 MeV neutron profile when tungsten peaks on the outboard side of the plasma.

Keyword
tungsten, neutral beam, JET, asymmetry, neutron
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-251991 (URN)10.1088/0741-3335/57/4/045001 (DOI)000351637700013 ()
Available from: 2015-05-11 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
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