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Publications (10 of 13) Show all publications
Ström, P., Petersson, P., Rubel, M., Bergsåker, H., Bykov, I., Frassinetti, L., . . . et al., . (2019). Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, 516, 202-213
Open this publication in new window or tab >>Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall
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2019 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 202-213Article in journal (Refereed) Published
Abstract [en]

Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analyzed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 micrometer were indicated, but typical values were on the order of a few hundred nanometers. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 micrometer were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

Keywords
Fusion, Tokamak, Plasma-wall interactions, ToF-ERDA, NRA, SEM
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-240616 (URN)10.1016/j.jnucmat.2018.11.027 (DOI)000458897100020 ()2-s2.0-85060313456 (Scopus ID)
Note

QC 20190125

Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-08-08Bibliographically approved
Tholerus, E., Johnson, T. & Hellsten, T. (2017). FOXTAIL: Modeling the nonlinear interaction between Alfven eigenmodes and energetic particles in tokamaks. Computer Physics Communications, 214, 39-51
Open this publication in new window or tab >>FOXTAIL: Modeling the nonlinear interaction between Alfven eigenmodes and energetic particles in tokamaks
2017 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 214, p. 39-51Article in journal (Refereed) Published
Abstract [en]

FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfven eigenmodes in tokamaks with realistic geometries. The code Simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five dimensional phase space representing the energetic particle distribution. Action angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
Keywords
Magnetohydrodynamic waves, Tokamaks, Fast particle effects, Nonlinear dynamics
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-205427 (URN)10.1016/j.cpc.2017.01.007 (DOI)000397358400005 ()2-s2.0-85011005108 (Scopus ID)
Funder
Swedish Research Council, 621-2011-5387
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-06-08Bibliographically approved
Tholerus, E., Johnson, T. & Hellsten, T. (2016). Modelling the Dynamics of Energetic Ions and MHD Modes Influenced by ICRH. KTH Royal Institute of Technology
Open this publication in new window or tab >>Modelling the Dynamics of Energetic Ions and MHD Modes Influenced by ICRH
2016 (English)Report (Other academic)
Abstract [en]

FOXTAIL is a code used to describe the nonlinear interactions between toroidal Alfvén eigenmodes and an ensemble of resonant energetic particles in tokamaks with realistic geometries. This report introduces an extension of the code, including effects from ion cyclotron resonance heating (ICRH) of energetic ions using a quasilinear diffusion operator in adiabatic invariant space. First results of the effects of ICRH diffusion on the system consisting of a single Alfvén eigenmode linearly excited by resonant ions are presented. It is shown that the presence of ICRH diffusion allows for the mode amplitude to grow larger than in the case of nonlinear saturation in the absence of sources and sinks. Gradually increasing the strength of ICRH diffusion also decreases the linear growth rate of the mode. Both these phenomena are previously observed also for the case of a finite phase decorrelation operator in bump-on-tail systems with a single eigenmode.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016
Series
TRITA-EE, ISSN 1653-5146 ; 2016:142
Keywords
Monte Carlo model, wave-particle interactions, bump-on-tail instabilities, nonlinear dynamics, toroidal Alfvén eigenmodes, ion cyclotron resonance heating
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-192924 (URN)
Funder
Swedish Research Council, 621-2011-5387
Note

QC 20160927

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2016-09-27Bibliographically approved
Tholerus, E., Hellsten, T. & Johnson, T. (2015). A bump-on-tail model for Alfvén eigenmodes in toroidal plasmas. In: : . Paper presented at 14th IAEA Technical Meeting on “Energetic Particles in Magnetic Confinement Systems”, Vienna, Austria, September 1 - 4, 2015. International Atomic Energy Agency
Open this publication in new window or tab >>A bump-on-tail model for Alfvén eigenmodes in toroidal plasmas
2015 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Presented is a numerical model for solving the nonlinear dynamics of Alfvén eigenmodes and energetic ions self-consistently. The model is an extension of a previous bump-on-tail model [1,2], taking into account particle orbits and wave fields in realistic toroidal geometries. The model can be used in conjunction with an orbit averaged Monte Carlo code that handles heating and current drive (similar to e.g. the SELFO code), which enables modeling of the effects of MHD activity on plasma heating. For rapid particle tracing, the unperturbed guiding center orbits are described with canonical action-angle coordinates [3], and the perturbed Hamiltonian for wave-particle interaction is included as Fourier components in the same angles [4]. This allows the numerical integrator to take time steps over several transit periods, which efficiently resolves the relevant time scales for nonlinear wave-particle dynamics. The wave field is modeled by a static eigenfunction and a dynamic complex amplitude driven by the interactions with resonant and non-resonant particles.

[1] E. Tholerus, T. Hellsten and T. Johnson, Phys. Plasmas 22, 082106 (2015)

[2] S. Tholerus, T. Hellsten and T. Johnson, J. Phys.: Conf. Ser. 561, 012019 (2014)

[3] A. N. Kaufman, Phys. Fluids 15, 1063 (1972)

[4] H. L. Berk, B. N. Breizman and M. S. Pekker, Nucl. Fusion 35, 1713 (1995)

Place, publisher, year, edition, pages
International Atomic Energy Agency, 2015
Keywords
Monte Carlo model, wave-particle interactions, bump-on-tail instabilities, toroidal Alfvén eigenmodes, nonlinear dynamics
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-192940 (URN)
Conference
14th IAEA Technical Meeting on “Energetic Particles in Magnetic Confinement Systems”, Vienna, Austria, September 1 - 4, 2015
Funder
Swedish Research Council, 621-2011-5387
Note

QC 20160927

Available from: 2016-09-23 Created: 2016-09-23 Last updated: 2016-09-27Bibliographically approved
Graves, J. P., Lennholm, M., Chapman, I. T., Lerche, E., Reich, M., Alper, B., . . . Tsalas, M. (2015). Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall. Plasma Physics and Controlled Fusion, 57(1), 014033
Open this publication in new window or tab >>Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall
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2015 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 1, p. 014033-Article in journal (Refereed) Published
Abstract [en]

New experiments at JET with the ITER-like wall show for the first time that ITER-relevant low field side resonance first harmonic ion cyclotron resonance heating (ICRH) can be used to control sawteeth that have been initially lengthened by fast particles. In contrast to previous (Graves et al 2012 Nat. Commun. 3 624) high field side resonance sawtooth control experiments undertaken at JET, it is found that the sawteeth of L-mode plasmas can be controlled with less accurate alignment between the resonance layer and the sawtooth inversion radius. This advantage, as well as the discovery that sawteeth can be shortened with various antenna phasings, including dipole, indicates that ICRH is a particularly effective and versatile tool that can be used in future fusion machines for controlling sawteeth. Without sawtooth control, neoclassical tearing modes (NTMs) and locked modes were triggered at very low normalised beta. High power H-mode experiments show the extent to which ICRH can be tuned to control sawteeth and NTMs while simultaneously providing effective electron heating with improved flushing of high Z core impurities. Dedicated ICRH simulations using SELFO, SCENIC and EVE, including wide drift orbit effects, explain why sawtooth control is effective with various antenna phasings and show that the sawtooth control mechanism cannot be explained by enhancement of the magnetic shear. Hybrid kinetic-magnetohydrodynamic stability calculations using MISHKA and HAGIS unravel the optimal sawtooth control regimes in these ITER relevant plasma conditions.

Keywords
sawteeth, ICRH, tungsten, NTMs, tokamaks, MHD
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-160760 (URN)10.1088/0741-3335/57/1/014033 (DOI)000348194900034 ()2-s2.0-84913580741 (Scopus ID)
Note

QC 20150303

Available from: 2015-03-03 Created: 2015-02-27 Last updated: 2017-12-04Bibliographically approved
Tholerus, E. (2015). The dynamics of Alfvén eigenmodes excited by energetic ions in toroidal plasmas. (Licentiate dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>The dynamics of Alfvén eigenmodes excited by energetic ions in toroidal plasmas
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Experiments for the development of fusion power that are based on magnetic confinement deal with plasmas that inevitably contain energetic (non-thermal) particles. These particles come e.g. from fusion reactions or from external heating of the plasma. Ensembles of energetic ions can excite plasma waves in the Alfvén frequency range to such an extent that the resulting wave fields redistribute the energetic ions, and potentially eject them from the plasma. The redistribution of ions may cause a substantial reduction heating efficiency, and it may damage the inner walls and other components of the vessel. Understanding the dynamics of such instabilities is necessary to optimise the operation of fusion experiments and of future fusion power plants.

A Monte Carlo model that describes the nonlinear wave-particle dynamics in a toroidal plasma has been developed to study the excitation of the abovementioned instabilities. A decorrelation of the wave-particle phase is added in order to model stochasticity of the system (e.g. due to collisions between particles). Based on the nonlinear description with added phase decorrelation, a quasilinear version of the model has been developed, where the phase decorrelation has been replaced by a quasilinear diffusion coefficient in particle energy. When the characteristic time scale for macroscopic phase decorrelation becomes similar to or shorter than the time scales of nonlinear wave-particle dynamics, the two descriptions quantitatively agree on a macroscopic level. The quasilinear model is typically less computationally demanding than the nonlinear model, since it has a lower dimensionality of phase space.

In the presented studies, several effects on the macroscopic wave-particle dynamics by the presence of phase decorrelation have been theoretically and numerically analysed, e.g. effects on the growth and saturation of the wave amplitude, and on the so called frequency chirping events with associated hole-clump pair formation in particle phase space. Several effects coming from structures of the energy distribution of particles around the wave-particle resonance has also been studied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. xiv, 71
Series
TRITA-EE, ISSN 1653-5146 ; 2015:014
Keywords
Fusion plasma physics, tokamak, wave-particle interactions, toroidal Alfvén eigenmodes, bump-on-tail instabilities, magnetohydrodynamics, nonlinear dynamics, quasilinear dynamics, Hamiltonian mechanics, Monte Carlo method
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-163127 (URN)978-91-7595-499-8 (ISBN)
Presentation
2015-05-22, Seminar Room, 3rd floor, Teknikringen 31, Stockholm, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2011-5387
Note

QC 20150330

Available from: 2015-03-30 Created: 2015-03-27 Last updated: 2015-03-30Bibliographically approved
Tholerus, E., Hellsten, T. & Johnson, T. (2015). The effects of phase decorrelation on the dynamics of the bump-on-tail instability. Physics of Plasmas, 22(8), Article ID 082106.
Open this publication in new window or tab >>The effects of phase decorrelation on the dynamics of the bump-on-tail instability
2015 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 8, article id 082106Article in journal (Refereed) Published
Abstract [en]

The dynamics of the bump-on-tail instability has been studied. The novelty of the work is the analysis of how the bump-on-tail dynamics is affected by an extrinsic stochastisation of the phase of the wave-particle interaction; here referred to as phase decorrelation. For this purpose, a nonlinear Monte Carlo model has been developed. When the characteristic time scale for macroscopic phase decorrelation becomes shorter than time scales of nonlinear wave-particle dynamics, the system may be described quasilinearly, with the phase decorrelation being replaced by a quasilinear diffusion coefficient in particle energy. A purely quasilinear Monte Carlo model, which is typically less computationally demanding than the fully nonlinear description due to the reduced dimensionality of phase space, has been developed for comparison. In this paper, parameter regimes, where the nonlinear and the quasilinear descriptions quantitatively agree on a macroscopic level, have been investigated, using combined theoretical and numerical analyses. Qualitative effects on the macroscopic dynamics by the presence of phase decorrelation and/or by structures of the energy distribution function in the proximity of the wave-particle resonance are also studied.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
Keywords
Monte Carlo model, wave-particle interactions, bump-on-tail instabilities, nonlinear dynamics, quasilinear dynamics, toroidal Alfvén eigenmodes
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-161935 (URN)10.1063/1.4928094 (DOI)000360647600010 ()2-s2.0-84938790389 (Scopus ID)
Funder
Swedish Research Council, 621-2011-5387
Note

QC 20151005. Updated from submitted to published.

Available from: 2015-03-27 Created: 2015-03-19 Last updated: 2017-12-04Bibliographically approved
Chapman, I. T., Graves, J. P., Lennholm, M., Faustin, J., Lerche, E., Johnson, T. & Tholerus, S. (2015). The merits of ion cyclotron resonance heating schemes for sawtooth control in tokamak plasmas. Journal of Plasma Physics, 81(06), Article ID 365810601.
Open this publication in new window or tab >>The merits of ion cyclotron resonance heating schemes for sawtooth control in tokamak plasmas
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2015 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, no 06, article id 365810601Article in journal (Refereed) Published
Abstract [en]

JET experiments have compared the efficacy of low-and high field side ion cyclotron resonance heating (ICRH) as an actuator to deliberately minimise the sawtooth period. It is found that low-field side ICRH with low minority concentration is optimal for saw tooth control for two main reasons. Firstly, low-field side heating means that any toroidal phasing of the ICRH (-90 degrees, +90 degrees or dipole) has a destabilising effect on the sawteeth, meaning that dipole phasing can be employed, since tins is preferable due to less plasma wall interaction from Resonant Frequency (RI) sheaths. Secondly, the resonance position of the low field side ICRH does not have to be very accurately placed to achieve saw tooth control, relaxing the requirement for real-time control of the RF frequency. These empirical observations have been confirmed by hybrid kinetic-magnetohydrodynamic modelling, and suggest that the ICRH antenna design for ITER is well positioned to provide a control actuator capable of having a significant effect on the sawtooth behaviour.

Place, publisher, year, edition, pages
Cambridge University Press, 2015
Keywords
CURRENT DRIVE, TOROIDAL PLASMAS, STABILITY, MODES, ITER, STABILIZATION, PERIOD, PHASE, JET
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-181391 (URN)10.1017/S0022377815000987 (DOI)000367574600003 ()2-s2.0-84944342424 (Scopus ID)
Note

QC 20160201

Available from: 2016-02-01 Created: 2016-02-01 Last updated: 2017-11-30Bibliographically approved
Tholerus, S., Hellsten, T. & Johnson, T. J. (2014). Comparisons of the nonlinear and the quasilinear model for the bump-on-tail instability with phase decorrelation. In: : . Paper presented at Joint Varenna-Lausanne International Workshop on the Theory of Fusion Plasmas, SEP 01-05, 2014, Varenna, ITALY. , 561
Open this publication in new window or tab >>Comparisons of the nonlinear and the quasilinear model for the bump-on-tail instability with phase decorrelation
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The dynamics of discrete global modes in a toroidal plasma interacting with an energetic particle distribution is studied, and in particular when the dynamics of the system using the nonlinear and quasilinear descriptions are macroscopically similar. The dynamics can be described with a nonlinear bump-on-tail model in a two-dimensional phase space of particles. A Monte Carlo framework is developed for this model with an included decorrelation of the wave-particle phase, which is used to model extrinsic stochastisation of the wave-particle interactions. From this description, a quasilinear version of the model is also developed, which is described by a diffusive process in energy space due to the added phase decorrelation. Due to the reduced dimensionality of phase space, the quasilinear description is typically less computationally demanding than the nonlinear description. The purpose of the studies is to find conditions when a quasilinear model sufficiently describes the same phenomena of the wave-plasma interactions as a nonlinear model does. Via numerical and theoretical parameter studies, regimes where the two models overlap macroscopically are found. These regimes exist above a given threshold of the strength of the decorrelation, where coherent phase space structures are destroyed on time scales shorter than characteristic time scales of nonlinear particle motion in phase space close to the wave-particle resonance. Specifically for the quasilinear model, a theoretical value of the time scale of quasilinear flattening is derived and numerically verified.

Series
Journal of Physics: Conference Series, ISSN 1742-6588
Keywords
Dynamics, Time measurement, Wave plasma interactions
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-159056 (URN)10.1088/1742-6596/561/1/012019 (DOI)000346423600019 ()2-s2.0-84919338077 (Scopus ID)
Conference
Joint Varenna-Lausanne International Workshop on the Theory of Fusion Plasmas, SEP 01-05, 2014, Varenna, ITALY
Note

QC 20150122

Available from: 2015-01-22 Created: 2015-01-20 Last updated: 2017-03-24Bibliographically approved
Tholerus, S. & Hellsten, T. (2014). On the Coupling of Waves for FWCD. In: Radiofrequency power in plasmas: . Paper presented at 20th Topical Conference on Radio Frequency Power in Plasmas, JUN 25-28, 2013, Sorrento, ITALY (pp. 330-333). , 1580
Open this publication in new window or tab >>On the Coupling of Waves for FWCD
2014 (English)In: Radiofrequency power in plasmas, 2014, Vol. 1580, p. 330-333Conference paper, Published paper (Refereed)
Abstract [en]

Coupling of an ICRF antenna to fast magnetosonic waves in a toroidal plasma is studied, considering incomplete damping of waves and passive conducting elements, e.g. conducting limiters, near the antenna. The system is characterized by coupling to a broad spectrum of partially overlapping resonant modes, whose frequency widths are due to finite damping. Small variations of plasma parameters, in particular the plasma density, can change the coupling to individual modes significantly. Therefore, a statistical analysis of the coupling is required. Currents in passive conductors near the antenna, which are induced, in particular by resonant modes, redistribute the coupling to on- and off-resonant modes. A statistical analysis is made to study how coupling to a large set of modes varies with respect to continuous variation of plasma parameters. At low single pass damping it is found that the coupling spectrum can be significantly modified by passive conducting components. This affects the directivity of the launched spectrum, which is important for fast wave current drive (FWCD).

Series
AIP Conference Proceedings, ISSN 0094-243X
Keywords
Fast Wave Current Drive, ICRF, Modeling
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-149997 (URN)10.1063/1.4864555 (DOI)000339626400060 ()2-s2.0-84906330004 (Scopus ID)978-0-7354-1210-1 (ISBN)
Conference
20th Topical Conference on Radio Frequency Power in Plasmas, JUN 25-28, 2013, Sorrento, ITALY
Note

QC 20140829

Available from: 2014-08-29 Created: 2014-08-29 Last updated: 2016-09-27Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3262-1958

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