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BETA
Ratynskaia, Svetlana V.ORCID iD iconorcid.org/0000-0002-6712-3625
Alternative names
Publications (10 of 93) Show all publications
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
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
Bykov, I., Rudakov, D. L., Ratynskaia, S. V., Tolias, P., De Angeli, M., Hollmann, E. M., . . . Riva, G. (2017). Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D. NUCLEAR MATERIALS AND ENERGY, 12, 379-385
Open this publication in new window or tab >>Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 379-385Article in journal (Refereed) Published
Abstract [en]

Transient heat load tests have been conducted in the lower divertor of DIII-D using DiMES manipulator in order to study the behavior of dust on tungsten Plasma Facing Components (PFCs) during ELMy H-mode discharges. Samples with pre- adhered, pre- characterized dust have been exposed at the outer strike point (OSP) in a series of discharges with varied intra-(inter-) ELM heat fluxes. We used C dust because of its high sublimation temperature and non-metal properties. Al dust as a surrogate for Be and W dust were employed as relevant to that in the ITER divertor. The poor initial thermal contact between the substrate and the particles led to overheating, sublimation and shrinking of the carbon dust, and wetting induced coagulation of Al dust. Little modification of the W dust was observed. An enhanced surface adhesion and improvement of the thermal contact of C and Al dust were the result of exposure. A post mortem "adhesive tape" sampling showed that 70% of Al, <5% of W and C particles could not be removed from the surface owing to the improved adhesion. Al and C but not W particles that could be lifted had W inclusions indicating damage to the substrate. This suggests that non destructive methods may be inefficient for removal of dust in ITER.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220632 (URN)10.1016/j.nme.2017.05.006 (DOI)000417293300057 ()2-s2.0-85020815010 (Scopus ID)
Note

QC 20180112

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-12Bibliographically approved
Komm, M., Ratynskaia, S., Tolias, P., Cavalier, J., Dejarnac, R., Gunn, J. P. & Podolnik, A. (2017). On thermionic emission from plasma-facing components in tokamak-relevant conditions. Plasma Physics and Controlled Fusion, 59(9), Article ID 094002.
Open this publication in new window or tab >>On thermionic emission from plasma-facing components in tokamak-relevant conditions
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2017 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 9, article id 094002Article in journal (Refereed) Published
Abstract [en]

The first results of particle-in-cell simulations of the electrostatic sheath and magnetic pre-sheath of thermionically emitting planar tungsten surfaces in fusion plasmas are presented. Plasma conditions during edge localized modes (ELMs) and during inter-ELM periods have been considered for various inclinations of the magnetic field and for selected surface temperatures. All runs have been performed under two assumptions for the sheath potential drop; fixed or floating. The primary focus lies on the evaluation of the escaping thermionic current and the quantification of the suppression due to the combined effects of space-charge and Larmor gyration. When applicable, the results are compared with the predictions of analytical models. The heat balance in the presence of thermionic emission as well as the contribution of the escaping thermionic current to surface cooling are also investigated. Regimes are identified where emission needs to be considered in the energy budget.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
tungsten, tokamak, thermionic emission, plasma facing components, particle-in-cell melting
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-211586 (URN)10.1088/1361-6587/aa78c4 (DOI)000405563900001 ()2-s2.0-85026767447 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20170815

Available from: 2017-08-15 Created: 2017-08-15 Last updated: 2017-08-15Bibliographically approved
De Angeli, M., Tolias, P., Ratynskaia, S. V., Ripamonti, D., Riva, G., Bardin, S., . . . De Temmerman, G. (2017). Remobilization of tungsten dust from castellated plasma-facing components. NUCLEAR MATERIALS AND ENERGY, 12, 536-540
Open this publication in new window or tab >>Remobilization of tungsten dust from castellated plasma-facing components
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 536-540Article in journal (Refereed) Published
Abstract [en]

Studies of tungsten dust remobilization from castellated plasma-facing components can shed light to whether gaps constitute a dust accumulation site with important implications for monitoring but also removal. Castellated structures of ITER relevant geometry that contained pre-adhered tungsten dust of controlled deposition profile have been exposed in the Pilot-PSI linear device. The experiments were performed under steady state and transient plasma conditions, as well as varying magnetic field topologies. The results suggest that dust remobilization from the plasma-facing monoblock surface can enhance dust trapping in the gaps and that tungsten dust is efficiently trapped inside the gaps.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220640 (URN)10.1016/j.nme.2017.01.021 (DOI)000417293300084 ()2-s2.0-85014656227 (Scopus ID)
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-11Bibliographically approved
Komm, M., Tolias, P., Ratynskaia, S. V., Dejarnac, R., Gunn, J. P., Krieger, K., . . . Panek, R. (2017). Simulations of thermionic suppression during tungsten transient melting experiments. Paper presented at 16th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC), MAY, 2017, GERMANY. Physica Scripta, T170, Article ID 014069.
Open this publication in new window or tab >>Simulations of thermionic suppression during tungsten transient melting experiments
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2017 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, article id 014069Article in journal (Refereed) Published
Abstract [en]

Plasma-facing components receive enormous heat fluxes under steady state and especially during transient conditions that can even lead to tungsten (W) melting. Under these conditions, the unimpeded thermionic current density emitted from the W surfaces can exceed the incident plasma current densities by several orders of magnitude triggering a replacement current which drives melt layer motion via the J x B force. However, in tokamaks, the thermionic current is suppressed by space-charge effects and prompt re-deposition due to gyro-rotation. We present comprehensive results of particle-in-cell modelling using the 2D3V code SPICE2 for the thermionic emissive sheath of tungsten. Simulations have been performed for various surface temperatures and selected inclinations of the magnetic field corresponding to the leading edge and sloped exposures. The surface temperature dependence of the escaping thermionic current and its limiting value are determined for various plasma parameters; for the leading edge geometry, the results agree remarkably well with the Takamura analytical model. For the sloped geometry, the limiting value is observed to be proportional to the thermal electron current and a simple analytical expression is proposed that accurately reproduces the numerical results.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220610 (URN)10.1088/1402-4896/aa9209 (DOI)000417694700014 ()
Conference
16th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC), MAY, 2017, GERMANY
Note

QC 20180115

Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-01-15Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-6712-3625

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