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Hellesen, Carl
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Publications (10 of 102) Show all publications
Eriksson, J., Hellesen, C., Binda, F., Cecconello, M., Conroy, S., Ericsson, G., . . . Tardocchi, M. (2019). Measuring fast ions in fusion plasmas with neutron diagnostics at JET. Plasma Physics and Controlled Fusion, 61(1), Article ID 014027.
Open this publication in new window or tab >>Measuring fast ions in fusion plasmas with neutron diagnostics at JET
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2019 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 1, article id 014027Article in journal (Refereed) Published
Abstract [en]

Fast ions in fusion plasmas often leave characteristic signatures in the neutron emission from the plasma. In this paper, we show how neutron measurements can be used to study fast ions and give examples of physics results obtained on present day tokamaks. The focus is on measurements with dedicated neutron spectrometers and with compact neutron detectors used in each channel of neutron profile monitors. A measured neutron spectrum can be analyzed in several different ways, depending on the physics scenario under consideration. Gross features of a fast ion energy distribution can be studied by applying suitably chosen thresholds to the measured spectrum, thus probing ions with different energies. With this technique it is possible to study the interaction between fast ions and MHD activity, such as toroidal Alfven eigenmodes (TAEs) and sawtooth instabilities. Quantitative comparisons with modeling can be performed by a direct computation of the neutron emission expected from a given fast ion distribution. Within this framework it is also possible to determine physics parameters, such as the supra-thermal fraction of the neutron emission, by fitting model parameters to the data. A detailed, model-independent estimate of the fast ion distribution can be obtained by analyzing the data in terms of velocity space weight functions. Using this method, fast ion distributions can be resolved in both energy and pitch by combining neutron and gamma-ray measurements obtained along several different sightlines. Fast ion measurements of the type described in this paper will also be possible at ITER, provided that the spectrometers have the dynamic range required to resolve the fast ion spectral features in the presence of the dominating thermonuclear neutron emission. A dedicated high-resolution neutron spectrometer has been designed for this purpose.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
fast ions, tokamaks, neutron diagnostics, plasma heating, MHD instabilities
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-371109 (URN)10.1088/1361-6587/aad8a6 (DOI)000450981300009 ()
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2018-12-20Bibliographically approved
Hellesen, C., Mantsinen, M., Conroy, S., Ericsson, G., Eriksson, J., Kiptily, V. & Nabais, F. (2018). Analysis of resonant fast ion distributions during combined ICRF and NBI heating with transients using neutron emission spectroscopy. Nuclear Fusion, 58(5), Article ID 056021.
Open this publication in new window or tab >>Analysis of resonant fast ion distributions during combined ICRF and NBI heating with transients using neutron emission spectroscopy
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 5, article id 056021Article in journal (Refereed) Published
Abstract [en]

ICRF heating at the fundamental cyclotron frequency of a hydrogen minority ion species also gives rise to a partial power absorption by deuterium ions at their second harmonic resonance. This paper studies the deuterium distributions resulting from such 2nd harmonic heating at JET using neutron emission spectroscopy data from the time of flight spectrometer TOFOR. The fast deuterium distributions are obtained over the energy range 100 keV to 2 MeV. Specifically, we study how the fast deuterium distributions vary as ICRF heating is used alone as well as in combination with NBI heating. When comparing the different heating scenarios, we observed both a difference in the shapes of the distributions as well as in their absolute level. The differences are most pronounced below 0.5 MeV. Comparisons are made with corresponding distributions calculated with the code PION. We find a good agreement between the measured distributions and those calculated with PION, both in terms of their shapes as well as their amplitudes. However, we also identified a period with signs of an inverted fast ion distribution, which showed large disagreements between the modeled and measured results. Resonant interactions with tornado modes, i.e. core localized toroidal alfven eigenmodes (TAEs), are put forward as a possible explanation for the inverted distribution.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-319414 (URN)10.1088/1741-4326/aab4ab (DOI)000428454700003 ()
Available from: 2017-04-04 Created: 2017-04-04 Last updated: 2018-06-20Bibliographically approved
Salewski, M., Nocente, M., Jacobsen, A. S., Binda, F., Cazzaniga, C., Eriksson, J., . . . Tardocchi, M. (2018). Bayesian Integrated Data Analysis of Fast-Ion Measurements by Velocity-Space Tomography. Paper presented at 2nd International Atomic Energy Agency (IAEA) Technical Meeting (TM) on Fusion Data Processing, Validation, and Analysis (IAEA-TM), MAY 30-JUN 02, 2017, Massachusetts Inst Technol Campus, Samberg Conf Ctr, Cambridge, MA. Fusion science and technology, 74(1-2), 23-36
Open this publication in new window or tab >>Bayesian Integrated Data Analysis of Fast-Ion Measurements by Velocity-Space Tomography
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2018 (English)In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 74, no 1-2, p. 23-36Article in journal (Refereed) Published
Abstract [en]

Bayesian integrated data analysis combines measurements from different diagnostics to jointly measure plasma parameters of interest such as temperatures, densities, and drift velocities. Integrated data analysis of fast-ion measurements has long been hampered by the complexity of the strongly non-Maxwellian fast-ion distribution functions. This has recently been overcome by velocity-space tomography. In this method two-dimensional images of the velocity distribution functions consisting of a few hundreds or thousands of pixels are reconstructed using the available fast-ion measurements. Here we present an overview and current status of this emerging technique at the ASDEX Upgrade tokamak and the JET toamak based on fast-ion D-alpha spectroscopy, collective Thomson scattering, gamma-ray and neutron emission spectrometry, and neutral particle analyzers. We discuss Tikhonov regularization within the Bayesian framework. The implementation for different types of diagnostics as well as the uncertainties are discussed, and we highlight the importance of integrated data analysis of all available detectors.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS INC, 2018
Keywords
Tokamaks, fast ions, velocity-space tomography
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-361010 (URN)10.1080/15361055.2017.1380482 (DOI)000436997000004 ()
Conference
2nd International Atomic Energy Agency (IAEA) Technical Meeting (TM) on Fusion Data Processing, Validation, and Analysis (IAEA-TM), MAY 30-JUN 02, 2017, Massachusetts Inst Technol Campus, Samberg Conf Ctr, Cambridge, MA
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2018-11-26Bibliographically approved
Åberg Lindell, M., Andersson, P., Grape, S., Hellesen, C., Håkansson, A. & Eriksson, M. (2018). Discrimination of irradiated MOX fuel from UOX fuel by multivariate statistical analysis of simulated activities of gamma-emitting isotopes. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 885, 67-78
Open this publication in new window or tab >>Discrimination of irradiated MOX fuel from UOX fuel by multivariate statistical analysis of simulated activities of gamma-emitting isotopes
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2018 (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. 885, p. 67-78Article in journal (Refereed) Published
Abstract [en]

This paper investigates how concentrations of certain fission products and their related gamma-ray emissions can be used to discriminate between uranium oxide (UOX) and mixed oxide (MOX) type fuel. Discrimination of irradiated MOX fuel from irradiated UOX fuel is important in nuclear facilities and for transport of nuclear fuel, for purposes of both criticality safety and nuclear safeguards. Although facility operators keep records on the identity and properties of each fuel, tools for nuclear safeguards inspectors that enable independent verification of the fuel are critical in the recovery of continuity of knowledge, should it be lost. A discrimination methodology for classification of UOX and MOX fuel, based on passive gamma-ray spectroscopy data and multivariate analysis methods, is presented. Nuclear fuels and their gamma-ray emissions were simulated in the Monte Carlo code Serpent, and the resulting data was used as input to train seven different multivariate classification techniques. The trained classifiers were subsequently implemented and evaluated with respect to their capabilities to correctly predict the classes of unknown fuel items. The best results concerning successful discrimination of UOX and MOX-fuel were acquired when using non-linear classification techniques, such as the k nearest neighbors method and the Gaussian kernel support vector machine. For fuel with cooling times up to 20 years, when it is considered that gamma-rays from the isotope  134Cs can still be efficiently measured, success rates of 100% were obtained. A sensitivity analysis indicated that these methods were also robust.

Keywords
Spent nuclear fuel, MOX, Gamma spectroscopy, Multivariate analysis, Classification
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-337676 (URN)10.1016/j.nima.2017.12.020 (DOI)000424740800009 ()
Funder
Swedish Research Council, VR 621-2009-3991Swedish Radiation Safety Authority, SSM2016-661
Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-04-19Bibliographically approved
Krasilnikov, A. V., Kiptily, V., Lerche, E., Van Eester, D., Afanasyev, V. I., Giroud, C., . . . Mironov, M. I. (2018). Evidence of Be-9 + p nuclear reactions during 2 omega(CH) and hydrogen minority ICRH in JET-ILW hydrogen and deuterium plasmas. Nuclear Fusion, 58(2), Article ID 026033.
Open this publication in new window or tab >>Evidence of Be-9 + p nuclear reactions during 2 omega(CH) and hydrogen minority ICRH in JET-ILW hydrogen and deuterium plasmas
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 2, article id 026033Article in journal (Refereed) Published
Abstract [en]

The intensity of Be-9 + p nuclear fusion reactions was experimentally studied during second harmonic (2 omega CH) ion-cyclotron resonance heating (ICRH) and further analyzed during fundamental hydrogen minority ICRH of JET-ILW hydrogen and deuterium plasmas. In relatively low-density plasmas with a high ICRH power, a population of fast H+ ions was created and measured by neutral particle analyzers. Primary and secondary nuclear reaction products, due to Be-9 + p interaction, were observed with fast ion loss detectors, gamma-ray spectrometers and neutron flux monitors and spectrometers. The possibility of using Be-9(p, d)2 alpha and Be-9(p, alpha)Li-6 nuclear reactions to create a population of fast alpha particles and study their behaviour in non-active stage of ITER operation is discussed in the paper.

Keywords
beryllium, proton, nuclear reactions, ICRH, alpha-particles
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-341566 (URN)10.1088/1741-4326/aa90c3 (DOI)000419796500003 ()
Available from: 2018-02-14 Created: 2018-02-14 Last updated: 2018-05-09Bibliographically approved
Gallart, D., Mantsinen, M. J., Challis, C., Frigione, D., Graves, J., Belonohy, E., . . . Valisa, M. (2018). Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating. Nuclear Fusion, 58(10), Article ID 106037.
Open this publication in new window or tab >>Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 10, article id 106037Article in journal (Refereed) Published
Abstract [en]

During the 2015-2016 JET campaigns, many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper, we review various key recent hybrid discharges and model the combined ICRF+NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions, allowing us to assess its impact on the neutron rate R-NT. For discharges carried out with a fixed ICRF antenna frequency and changing toroidal magnetic field to vary the resonance position, we evaluate the influence of the resonance position on the heating performance and central impurity control. The H concentration is varied between discharges in order to test its role in the heating performance. It is found that discharges with a resonance beyond similar to 0.15 m from the magnetic axis R-0 suffer from MHD activity and impurity accumulation in these plasma conditions. According to our modelling, the ICRF enhancement of R-NT increases with the ICRF power absorbed by deuterons as the H concentration decreases. We find that in the recent hybrid discharges, this ICRF enhancement varies due to a variation of H concentration and is in the range of 10%-25%. The modelling of a recent record high-performance hybrid discharge shows that ICRF fusion yield enhancement of similar to 30% and similar to 15% respectively can be achieved in the ramp-up phase and during the main heating phase. We extrapolate the results to DT and find that the best performing hybrid discharges correspond to an equivalent fusion power of similar to 7.0 MW in DT. Finally, an optimization analysis of the bulk ion heating for the DT scenario reveals around 15%-20% larger bulk ion heating for the He-3 minority scenario as compared to the H minority scenario.

Keywords
ICRF heating, NBI heating, JET hybrid plasmas, fusion enhancement
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-364135 (URN)10.1088/1741-4326/aad9ad (DOI)000443838500002 ()
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
Sahlberg, A., Hellesen, C., Eriksson, J., Conroy, S., Ericsson, G. & King, D. (2018). Propagating transport-code input parameter uncertainties with deterministic sampling. Plasma Physics and Controlled Fusion, 60(12), Article ID 125010.
Open this publication in new window or tab >>Propagating transport-code input parameter uncertainties with deterministic sampling
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2018 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 12, article id 125010Article in journal (Refereed) Published
Abstract [en]

A novel approach to uncertainty quantification in codes simulating fusion plasma, deterministic sampling (DS), is evaluated. This method uses a few carefully selected samples and can be used to propagate input parameter uncertainties through calculations where other sampling methods are unmanageable due to time constraints. The primary analysis is performed on the transport code TRANSP, but another faster code is also tested where a comparison with Monte Carlo sampling is made. The tests, performed with two pulses at the Joint European Torus (JET), show that even lower order DS will give a reliable estimation of the standard deviation of the calculated neutron rate. However, a higher order DS can give information about higher output moments, such as skewness an kurtosis. The TRANSP-simulated neutron rates of both examined pulses are found to have an uncertainty with an upward skewness, meaning input parameter uncertainties are can better explain an underestimation of the neutron rate than an overestimation. This information can, for example, be lead to a better benchmarking comparison between the measured and calculated neutron rates.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
fusion, transp, plasma, unscented transform, uncertainty quantification, deterministic sampling
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-369381 (URN)10.1088/1361-6587/aae80b (DOI)000449418100005 ()
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2019-01-15Bibliographically approved
Hellesen, C. & Qvist, S. (2017). Benchmark and demonstration of the CHD code for transient analysis of fast reactor systems. Annals of Nuclear Energy, 109, 712-719
Open this publication in new window or tab >>Benchmark and demonstration of the CHD code for transient analysis of fast reactor systems
2017 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 109, p. 712-719Article in journal (Refereed) Published
Abstract [en]

In this paper the dynamic thermal hydraulic fast reactor simulation code CHD is presented. The code is built around a scriptable object-oriented framework in the programming language Python to be able to flexibly describe different reactor geometries including thermal-hydraulics models of an arbitrary number of coolant channels as well as pumps, heat-exchangers and pools etc. In addition, custom objects such as the Autonomous Reactivity Control (ARC) system for enhanced passive safety are modeled in detail. In this paper we compare the performance of the CHD code with other similar fast reactor dynamics codes using a benchmark study of the European Sodium cooled Fast Reactor (ESFR). The results agree well, both qualitatively and quantitatively with the code benchmark. In addition, we demonstrate the code's ability to simulate the long-term asymptotic behavior of a neutronically shut down reactor in an unprotected loss of flow scenario using a model of the Advanced Burner Reactor (ABR). (C) 2017 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fast reactor, Thermal-hydraulics, Point-kinetics, Transient, Passive safety, ULOF
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-339705 (URN)10.1016/j.anucene.2017.05.031 (DOI)000418211500071 ()
Available from: 2018-01-26 Created: 2018-01-26 Last updated: 2018-01-26Bibliographically approved
Hellesen, C., Andersson Sundén, E., Conroy, S., Dzysiuk, N., Ericsson, G., Hjalmarsson, A., . . . Marcinkevicius, B. (2017). Conceptual design of a BackTOF neutron spectrometer for fuel ion ratio measurements at ITER. Nuclear Fusion, 57(6), Article ID 066021.
Open this publication in new window or tab >>Conceptual design of a BackTOF neutron spectrometer for fuel ion ratio measurements at ITER
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2017 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 6, article id 066021Article in journal (Refereed) Published
Abstract [en]

In this paper we present a conceptual design of a back scattering neutron time of flight spectrometer (BackTOF) for use at ITER. The proposed BackTOF design aims at fulfilling the requirements set on a neutron spectrometer system to be used for inferring the core fuel ion ratio in a DT plasma. Specifically we have investigated the requirements on the size, energy resolution, count rate capability, efficiency and signal to background ratio. These requirements are a compact size that fits in roughly 1 m3, an energy resolution of 4% or better, a count rate capability of at least 100 kHz, an efficiency of at least 10−5 and a signal to background ratio of 1000 or better.

Using a Monte Carlo model of the BackTOF spectrometer we find that the proposed BackTOF design is compact enough to be installed at ITER while being capable of achieving a resolution of about 4% FWHM with a count rate capability of 300 kHz and an efficiency at 1.25 10−3. This is sufficient for achieving the requirements on the fuel ion ratio at ITER. We also demonstrate how data acquisition systems capable of providing both timing and energy information can be used to effectively discriminate random background at high count rates.

Keywords
neutron spectroscopy, time of flight, burning plasma, fuel ion ratio
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-348803 (URN)10.1088/1741-4326/aa6937 (DOI)000425870000001 ()
Available from: 2018-05-04 Created: 2018-05-04 Last updated: 2018-05-04Bibliographically approved
Kazakov, Y. O. O., Possnert, G., Sjöstrand, H., Skiba, M., Weiszflog, M., Andersson Sundén, E., . . . Kazantzidis, V. (2017). Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, 13(10), 973-978
Open this publication in new window or tab >>Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
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2017 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 13, no 10, p. 973-978Article in journal (Refereed) Published
Abstract [en]

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed three-ion scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of He-3 ions to high energies in dedicated hydrogendeuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast He-3 ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, He-3-rich solar flares.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-359272 (URN)10.1038/NPHYS4167 (DOI)000412181200018 ()
Note

For a complete list of authors see http://dx.doi.org/10.1038/NPHYS4167

Available from: 2018-09-05 Created: 2018-09-05 Last updated: 2018-09-05Bibliographically approved
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