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BETA
Ratynskaia, Svetlana V.ORCID iD iconorcid.org/0000-0002-6712-3625
Alternative names
Publications (10 of 97) Show all publications
Tolias, T., Riva, G., De Angeli, M., Ratynskaia, S. V., Daminelli, G., Lungu, C. P. & Porosnicu, C. (2018). Adhesive force distributions for tungsten dust deposited on bulk tungsten and beryllium-coated tungsten surfaces. Nuclear Materials and Energy, 15, 55-63
Open this publication in new window or tab >>Adhesive force distributions for tungsten dust deposited on bulk tungsten and beryllium-coated tungsten surfaces
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2018 (English)In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 15, p. 55-63Article in journal (Refereed) Published
Abstract [en]

Comprehensive measurements of the adhesive force for tungsten dust adhered to tungsten surfaces have been performed with the electrostatic detachment method. Monodisperse spherical dust has been deposited with gas dynamics techniques or with gravity mimicking adhesion as it naturally occurs in tokamaks. The adhesive force is confirmed to follow the log-normal distribution and empirical correlations are proposed for the size-dependence of its mean and standard deviation. Systematic differences are observed between the two deposition methods and attributed to plastic deformation during sticking impacts. The presence of thin beryllium coatings on tungsten surfaces is demonstrated to barely affect adhesion.

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-238239 (URN)10.1016/j.nme.2018.05.013 (DOI)000435611400009 ()2-s2.0-85048178222 (Scopus ID)
Note

QC 20181031

Available from: 2018-10-31 Created: 2018-10-31 Last updated: 2018-10-31Bibliographically approved
Vignitchouk, L., Delzanno, G. L., Tolias, P. & Ratynskaia, S. V. (2018). Electron reflection effects on particle and heat fluxes to positively charged dust subject to strong electron emission. Physics of Plasmas, 25(6), Article ID 063702.
Open this publication in new window or tab >>Electron reflection effects on particle and heat fluxes to positively charged dust subject to strong electron emission
2018 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 6, article id 063702Article in journal (Refereed) Published
Abstract [en]

A new model describing dust charging and heating in unmagnetized plasmas in the presence of large electron emission currents is presented. By accounting for the formation of a potential well due to trapped emitted electrons when the dust is positively charged, this model extends the so-called OML+ approach, thus far limited to thermionic emission, by including electron-induced emission processes, and in particular low-energy quasi-elastic electron reflection. Revised semi-analytical formulas for the current and heat fluxes associated with emitted electrons are successfully validated against particle-in-cell simulations and predict an overall reduction of dust heating by up to a factor of 2. When applied to tungsten dust heating in divertor-like plasmas, the new model predicts that the dust lifetime increases by up to 80%, as compared with standard orbital-motion-limited estimates.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-232414 (URN)10.1063/1.5026384 (DOI)000437193700127 ()2-s2.0-85048606159 (Scopus ID)
Funder
EU, Horizon 2020, 633053Swedish Research CouncilLars Hierta Memorial Foundation
Note

QC 20180726

Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2018-07-26Bibliographically approved
Panarese, A., Bruno, D., Tolias, P., Ratynskaia, S. V., Longo, S. & de Angelis, U. (2018). Molecular dynamics calculation of the spectral densities of plasma fluctuations. Journal of Plasma Physics, 84(3), Article ID 905840308.
Open this publication in new window or tab >>Molecular dynamics calculation of the spectral densities of plasma fluctuations
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2018 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 3, article id 905840308Article in journal (Refereed) Published
Abstract [en]

Spectral densities of plasma fluctuations are calculated for the thermal case using classical molecular dynamics (MD) assuming Coulomb interactions and a short-range cutoff radius. The aim of the calculation is to verify limits and performances of such calculations in the light of possible generalizations, e.g. collisional or non-ideal plasmas. Results are presented for ideal, collisionless, fully ionized thermal plasmas. Comparison with the analytical theory reveals a generally satisfactory agreement with possibility for improvement when more strict numerical parameters are used albeit with a strong increase in computational cost. The largest deviations have been observed in the vicinity of the weakly damped eigenmodes. The agreement is strong in other parts of the spectrum, where Landau damping is prominent, and overcomes the effects stemming from the excess collisionality and coupling as well as from the exclusion of short-range collisions.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
plasma properties, plasma simulation
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-240044 (URN)10.1017/S0022377818000491 (DOI)000450962300009 ()
Funder
Swedish Research Council
Note

QC 20181210

Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2018-12-10Bibliographically approved
Thorén, E., Tolias, P., Ratynskaia, S. V., Pitts, R. A. & Krieger, K. (2018). Self-consistent description of the replacement current driving melt layer motion in fusion devices. Nuclear Fusion, 58(10), Article ID 106003.
Open this publication in new window or tab >>Self-consistent description of the replacement current driving melt layer motion in fusion devices
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 10, article id 106003Article in journal (Refereed) Published
Abstract [en]

The bulk replacement current density triggered by surface charge loss owing to thermionic emission leads to a volumetric Lorentz force which has been observed to drive macroscopic melt layer motion in transient tungsten melting tokamak experiments in which components of different geometries (deliberate leading edges and sloped surfaces) have been exposed to edge localized mode (ELM) pulsed heat loads in high power H-mode discharges. A self-consistent approach is formulated for the replacement current which is based on the magnetostatic limit of the resistive thermoelectric magnetohydrodynamic description of the liquid metal and results in a well-defined boundary value problem for the whole conductor. A new module is incorporated into the incompressible fluid dynamics code MEMOS-3D, which numerically solves the finite difference representation of the problem. The phenomenological approach, employed thus far to describe the replacement current, is demonstrated to be accurate for the sloped geometry but inadequate for the leading edge. MEMOS-3D simulations of very recent ASDEX-Upgrade leading edge experiments with the rigorous as well as the simplified approach are reported. For these simulations, the self-consistent approach predicts a fivefold reduction of the displaced material volume, a sevenfold reduction of the maximum peak height of displaced material and a different eroded surface morphology in comparison with the previously applied simplified approach.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018
Keywords
melting, tungsten, divertor, melt layer motion, MEMOS, thermionic emission
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-240196 (URN)10.1088/1741-4326/aad247 (DOI)000440040800003 ()2-s2.0-85053403050 (Scopus ID)
Note

QC 20181218

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2018-12-19Bibliographically approved
Vignitchouk, L., Ratynskaia, S., Kantor, M., Tolias, P., De Angeli, M., van der Meiden, H., . . . Banon, J.-P. (2018). Validating heat balance models for tungsten dust in cold dense plasmas. Plasma Physics and Controlled Fusion, 60(11), Article ID 115002.
Open this publication in new window or tab >>Validating heat balance models for tungsten dust in cold dense plasmas
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2018 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 11, article id 115002Article in journal (Refereed) Published
Abstract [en]

The first comparison of dust radius and surface temperature estimates, obtained from spectroscopic measurements of thermal radiation, with simulations of dust heating and vaporization by the MIGRAINe dust dynamics code is reported. The measurements were performed during controlled tungsten dust injection experiments in the cold and dense plasmas of Pilot-PSI, reproducing ITER divertor conditions. The comparison has allowed us to single out the dominating role of the work function contribution to the dust heating budget. However, in the plasmas of interest, dust was found to enter the strong vaporization regime, in which its temperature is practically insensitive to plasma properties and the various uncertainties in modeling. This makes the dust temperature a poor figure of merit for model validation purposes. On the other hand, simple numerical scalings obtained from orbital-motion-limited estimates were found to be remarkably robust and sufficient to understand the main physics at play in such cold and dense plasmas.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
tungsten, dust, orbital-motion-limited, Pilot-PSI
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235552 (URN)10.1088/1361-6587/aadbcb (DOI)000444743500002 ()
Funder
Swedish Research Council
Note

QC 20181002

Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2018-10-02Bibliographically approved
Riva, G., Tolias, P., Ratynskaia, S. V., Daminelli, G., Donde, R., De Angeli, M., . . . Pedroni, M. (2017). Adhesion measurements for tungsten dust deposited on tungsten surfaces. NUCLEAR MATERIALS AND ENERGY, 12, 593-598
Open this publication in new window or tab >>Adhesion measurements for tungsten dust deposited on tungsten surfaces
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 593-598Article in journal (Refereed) Published
Abstract [en]

The first experimental determination of the pull-off force for tungsten dust adhered to tungsten surfaces is reported. Dust deposition is conducted with gas dynamics methods in a manner that mimics sticking as it occurs in the tokamak environment. Adhesion measurements are carried out with the electrostatic detachment method. The adhesion strength is systematically characterized for spherical micron dust of different sizes and planar surfaces of varying roughness. The experimental pull-off force is nearly two orders of magnitude smaller than the predictions of contact mechanics models, but in strong agreement with the Van der Waals formula. A theoretical interpretation is provided that invokes the effects of nanometer-scale surface roughness for stiff materials such as tungsten.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220645 (URN)10.1016/j.nme.2016.11.009 (DOI)000417293300094 ()2-s2.0-85007022962 (Scopus ID)
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-11Bibliographically approved
Vignitchouk, L., Ratynskaia, S. V. & Tolias, P. (2017). Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas. Plasma Physics and Controlled Fusion, 59(10), Article ID 104002.
Open this publication in new window or tab >>Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas
2017 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 10, article id 104002Article in journal (Refereed) Published
Abstract [en]

A comprehensive analytical description is presented for the particle and heat fluxes collected by dust in dense magnetized plasmas. Compared to the widely used orbital motion limited theory, the suppression of cross-field transport leads to a strong reduction of the electron fluxes, while ion collection is inhibited by thin-sheath effects and the formation of a potential overshoot along the field lines. As a result, the incoming heat flux loses its sensitivity to the floating potential, thereby diminishing the importance of electron emission processes in dust survivability. Numerical simulations implementing the new model for ITER-like detached divertor plasmas predict a drastic enhancement of the dust lifetime.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
dust, droplets, dust heating, magnetized electron collection, thin-sheath ions
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-213756 (URN)10.1088/1361-6587/aa7c44 (DOI)000407750200001 ()2-s2.0-85029917782 (Scopus ID)
Note

QC 20170911

Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2017-09-11Bibliographically approved
Weinzettl, V., Matejicek, J., Ratynskaia, S. V., Tolias, P., De Angeli, M., Riva, G., . . . Peterka, M. (2017). Dust remobilization experiments on the COMPASS tokamak. Paper presented at 29th Symposium on Fusion Technology (SOFT), SEP 05-09, 2016, Prague, CZECH REPUBLIC. Fusion engineering and design, 124, 446-449
Open this publication in new window or tab >>Dust remobilization experiments on the COMPASS tokamak
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2017 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 124, p. 446-449Article in journal (Refereed) Published
Abstract [en]

Dust remobilization is one of the not yet fully understood mechanisms connected to the prompt erosion of material from plasma facing surfaces in fusion devices. As a part of a newly initiated cross-machine study, dust remobilization experiments have been performed on the COMPASS tokamak. Tungsten samples with well-defined deposited tungsten dust grains, prepared using a recently developed controlled pre-adhesion method, have been exposed to ELMy H-mode discharges as well as L-mode discharges with forced disruptions. Here we report on the technical aspects of the experiment realization as well as on the experimental results of dust remobilization. The latter is discussed in the light of data from other machines and a physical interpretation is suggested for the observed spatial localization of the dust remobilization activity. Evidence of rearrangement of isolated dust into clusters and strings is also presented.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keywords
Dust remobilization, Tungsten, Disruption, ELM, Plasma, Tokamak
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-221892 (URN)10.1016/j.fusengdes.2017.01.044 (DOI)000419411900094 ()2-s2.0-85011342779 (Scopus ID)
Conference
29th Symposium on Fusion Technology (SOFT), SEP 05-09, 2016, Prague, CZECH REPUBLIC
Note

QC 20180131

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2018-01-31Bibliographically approved
Tolias, P., Ratynskaia, S. V., Shalpegin, A., Vignitchouk, L., Brochard, F., De Angeli, M. & van der Meiden, H. (2017). Experimental validation of the analytical model for tungsten dust - wall mechanical impacts incorporated in the MIGRAINe dust dynamics code. NUCLEAR MATERIALS AND ENERGY, 12, 524-529
Open this publication in new window or tab >>Experimental validation of the analytical model for tungsten dust - wall mechanical impacts incorporated in the MIGRAINe dust dynamics code
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 524-529Article in journal (Refereed) Published
Abstract [en]

Mechanical dust-wall collisions are unavoidable in fusion devices and their accurate modeling is essential for the understanding of dust transport. The MIGRAINe dust dynamics code features analytical models addressing all facets of dust-surface impacts, some aspects of which have not been experimentally validated thus far. Dedicated dust injection experiments have been carried out in Pilot-PSI resulting to the visualization of in-plasma tungsten dust-surface impacts with an unprecedented resolution. They allowed for a calibration of key quantities of the MIGRAINe impact model.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220639 (URN)10.1016/j.nme.2017.01.007 (DOI)000417293300082 ()2-s2.0-85015661567 (Scopus ID)
Note

QC 20180112

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-12Bibliographically approved
Krieger, K., Sieglin, B., Balden, M., Coenen, J. W., Goeths, B., Laggner, F., . . . Tolias, P. (2017). Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade. Paper presented at 16th International Conference on Plasma-Facing Materials and Components for Fusion Applications, MAY 16-19, 2017, GERMANY. Physica Scripta, T170, Article ID 014030.
Open this publication in new window or tab >>Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade
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2017 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, article id 014030Article in journal (Refereed) Published
Abstract [en]

Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II system. The exposed sample was designed with an elevated sloped surface inclined against the incident magnetic field to increase the projected parallel power flux to a level were transient melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point to the sample location. As extension to previous melt studies in the new experiment both the current flow from the sample to vessel potential and the local surface temperature were measured with sufficient time resolution to resolve individual ELMs. The experiment provided for the first time a direct link of current flow and surface temperature during transient ELM events. This allows to further constrain the MEMOS melt motion code predictions and to improve the validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved samples confirms the decreased melt motion observed at shallower magnetic field line to surface angles compared to that at leading edges exposed to the parallel power flux.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
plasma-facing components, tungsten, melting, edge-localized modes
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-217722 (URN)10.1088/1402-4896/aa8be8 (DOI)000414120500030 ()
Conference
16th International Conference on Plasma-Facing Materials and Components for Fusion Applications, MAY 16-19, 2017, GERMANY
Note

QC 20171123

Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2017-11-23Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6712-3625

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