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Vignitchouk, LadislasORCID iD iconorcid.org/0000-0001-7796-1887
Alternative names
Publications (10 of 19) Show all publications
Sias, G., Frassinetti, L., Hellsten, T., Petersson, P., Rubel, M., Fridström, R., . . . Zychor, I. (2019). A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion engineering and design, 138, 254-266
Open this publication in new window or tab >>A locked mode indicator for disruption prediction on JET and ASDEX upgrade
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2019 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 138, p. 254-266Article in journal (Refereed) Published
Abstract [en]

The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different machines would facilitate the development of portable systems for disruption prediction, which is becoming of increasingly importance for the next tokamak generations. Moreover, the indicator allows us to overcome some intrinsic problems in the diagnostic system such as drift and offset. The behavior of the proposed indicator as disruption predictor, based on crossing optimized thresholds of the signal amplitude, has been analyzed using data of both JET and ASDEX Upgrade experiments. A thorough analysis of the disruption prediction performance shows how the indicator is able to recover some missed and tardy detections of the raw signal. Moreover, it intervenes and corrects premature or even wrong alarms due to, e.g., drifts and/or offsets.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Tokamak, Disruption prediction, Locked mode signal, Disruption indicators, Feature extraction
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-269602 (URN)10.1016/j.fusengdes.2018.11.021 (DOI)000457663100032 ()2-s2.0-85057571211 (Scopus ID)
Note

QC 20200407

Available from: 2020-04-07 Created: 2020-04-07 Last updated: 2020-04-07Bibliographically approved
Vignitchouk, L., Ratynskaia, S. V., Tolias, P., Pitts, R. A., De Temmerman, G., Lehnen, M. & Kiramov, D. (2019). Accumulation of beryllium dust in ITER diagnostic ports after off-normal events. Paper presented at 23rd International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI), JUN 18-22, 2018, Princeton Univ, Princeton, NJ. Nuclear Materials and Energy, 20, Article ID UNSP 100684.
Open this publication in new window or tab >>Accumulation of beryllium dust in ITER diagnostic ports after off-normal events
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2019 (English)In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 20, article id UNSP 100684Article in journal (Refereed) Published
Abstract [en]

Dust transport simulations are used to predict the effect of diagnostic ports on the in-vessel inventory of solid beryllium particles produced during mitigated disruptions in ITER. Beryllium dust is assumed to originate from the re-solidification of liquid droplets, which are initially ejected during transient first-wall melting events and subsequently interact with the disrupting plasma. The trajectories of droplets launched with various initial conditions, as well as the time evolution of their temperature and mass, are simulated until either complete vaporization or immobilization upon undergoing a sticking or splashing impact with the wall is realized. The results indicate that approximately 10% of the dust mass in the vessel can be expected to reside inside ports, in particular those located in the equatorial plane or in the lower outboard first wall.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Beryllium, Dust, Droplets, Disruptions
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-266196 (URN)10.1016/j.nme.2019.100684 (DOI)000500930800002 ()2-s2.0-85065446827 (Scopus ID)
Conference
23rd International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI), JUN 18-22, 2018, Princeton Univ, Princeton, NJ
Note

QC 20200110

Available from: 2020-01-10 Created: 2020-01-10 Last updated: 2020-01-10Bibliographically approved
Trier, E., Frassinetti, L., Fridström, R., Garcia Carrasco, A., Hellsten, T., Johnson, T., . . . Zuin, M. (2019). ELM-induced cold pulse propagation in ASDEX Upgrade. Plasma Physics and Controlled Fusion, 61(4), Article ID 045003.
Open this publication in new window or tab >>ELM-induced cold pulse propagation in ASDEX Upgrade
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2019 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 4, article id 045003Article in journal (Refereed) Published
Abstract [en]

In ASDEX Upgrade, the propagation of cold pulses induced by type-I edge localized modes (ELMs) is studied using electron cyclotron emission measurements, in a dataset of plasmas with moderate triangularity. It is found that the edge safety factor or the plasma current are the main determining parameters for the inward penetration of the T-e perturbations. With increasing plasma current the ELM penetration is more shallow in spite of the stronger ELMs. Estimates of the heat pulse diffusivity show that the corresponding transport is too large to be representative of the inter-ELM phase. Ergodization of the plasma edge during ELMs is a possible explanation for the observed properties of the cold pulse propagation, which is qualitatively consistent with non-linear magneto-hydro-dynamic simulations.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
ELMs, MHD instabilities, stochastic field, magnetic islands, cold pulse
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-245121 (URN)10.1088/1361-6587/aaf9c3 (DOI)000458986000002 ()2-s2.0-85064405933 (Scopus ID)
Note

QC 20190315

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2020-05-11Bibliographically approved
De Angeli, M., Lazzaro, E., Tolias, P., Ratynskaia, S. V., Vignitchouk, L., Castaldo, C., . . . Uccello, A. (2019). Pre-plasma remobilization of ferromagnetic dust in FTU and possible interference with tokamak operations. Nuclear Fusion, 59(10), Article ID 106033.
Open this publication in new window or tab >>Pre-plasma remobilization of ferromagnetic dust in FTU and possible interference with tokamak operations
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 10, article id 106033Article in journal (Refereed) Published
Abstract [en]

Experimental evidence of the pre-plasma remobilization of ferromagnetic dust in FTU is presented. Thomson scattering data and IR camera observations document the occurrence of intrinsic dust remobilization prior to discharge start-up and allow for a rough calculation of the average mobilized dust density. Exposures of calibrated extrinsic non-magnetic and ferromagnetic dust to sole magnetic field discharges reveal that the magnetic moment force is the main mobilizing force, as confirmed by theoretical estimates. Pre-plasma remobilization probabilities are computed for varying dust sizes. The impact of prematurely remobilized dust on the breakdown and burn-through start-up phases is investigated together with the discharge termination induced once the plasma plateau is established.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
magnetic dust, dust mobilization, discharge start-up, discharge breakdown, dust in tokamaks
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-261002 (URN)10.1088/1741-4326/ab369f (DOI)000484508000003 ()2-s2.0-85072714767 (Scopus ID)
Note

QC 20191010

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10Bibliographically approved
Tierens, W., Frassinetti, L., Hellsten, T., Petersson, P., Fridström, R., Garcia Carrasco, A., . . . et al., . (2019). Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments. Nuclear Fusion, 59(4), Article ID 046001.
Open this publication in new window or tab >>Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 4, article id 046001Article in journal (Refereed) Published
Abstract [en]

In this paper we validate the finite element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap antenna, and for a 4-strap WEST-like antenna. Although RAPLICASOL requires considerably fewer computational resources than TOPICA, we find that the predicted quantities of experimental interest (including reflection coefficients, coupling resistances, S- and Z-matrix entries, optimal matching settings, and even radiofrequency electric fields) are in good agreement provided we are careful to use the same geometry in both codes.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
ICRF, finite elements, simulation
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-243928 (URN)10.1088/1741-4326/aaf455 (DOI)000456197200001 ()2-s2.0-85064078268 (Scopus ID)
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2020-05-11Bibliographically 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
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 ()2-s2.0-85055574326 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20181002

Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-08-20Bibliographically 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
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
Ratynskaia, S. V., Tolias, P., De Angeli, M., Weinzettl, V., Matejicek, J., Bykov, I., . . . De Temmerman, G. (2017). Tungsten dust remobilization under steady-state and transient plasma conditions. NUCLEAR MATERIALS AND ENERGY, 12, 569-574
Open this publication in new window or tab >>Tungsten dust remobilization under steady-state and transient plasma conditions
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 569-574Article in journal (Refereed) Published
Abstract [en]

Remobilization is one of the most prominent unresolved fusion dust-relevant issues, strongly related to the lifetime of dust in plasma-wetted regions, the survivability of dust on hot plasma-facing surfaces and the formation of dust accumulation sites. A systematic cross-machine study has been initiated to investigate the remobilization of tungsten micron-size dust from tungsten surfaces implementing a newly developed technique based on controlled pre-adhesion by gas dynamics methods. It has been utilized in a number of devices and has provided new insights on remobilization under steady-state and transient conditions. The experiments are interpreted with contact mechanics theory and heat conduction models.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-220643 (URN)10.1016/j.nme.2016.10.021 (DOI)000417293300090 ()2-s2.0-85006994117 (Scopus ID)
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-05-23Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7796-1887

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