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  • 1.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Banon, Jean-Philippe
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 3, p. 035014-Article in journal (Refereed)
    Abstract [en]

    Experimental data on dust resident in the EXTRAP T2R reversed-field pinch are reported. Mobile dust grains are captured in situ by silicon collectors, whereas immobile grains are sampled post mortem from the wall by adhesive tape. The simulation of collection asymmetries by the MIGRAINe dust dynamics code in combination with the experimental results is employed to deduce some characteristics of the mechanism of intrinsic dust release. All evidence suggests that re-mobilization is dominant with respect to dust production.

  • 2. Lazzaro, E.
    et al.
    Proverbio, I.
    Nespoli, F.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Castaldo, C.
    Deangelis, U.
    Deangeli, M.
    Banon, Jean-Philippe
    KTH.
    Vignitchouk, Ladislas
    KTH.
    Transport and effects of ferromagnetic dust in a tokamak with a metallic vessel2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 12, p. 124043-Article in journal (Refereed)
    Abstract [en]

    Important physics effects in contemporary and future devices for magnetic fusion experiments depend on the interface with a 'composite' plasma, consisting of multiple ion species and heterogeneous dust with variable charge. A selection of processes related to dust and occurring in existing tokamaks is presented, focusing on new results on the physics of isolated micrometric ferromagnetic dust particles in the SOL of a tokamak with a metallic vessel of circular meridian cross section. Such particles in particular, in addition to usual forces, are subjected to magnetic dipole interaction with the ambient magnetic field and to strong evaporation effects at high surface temperatures. Moreover, preliminary results of inclusion of gaps in the vessel geometry suggest the possibility of dust trapping. Also reported are the effects of nanometre dust on plasma when the dust is to be considered as a plasma component.

  • 3.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bykov, Igor
    Rudakov, Dmitry
    De Angeli, Marco
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ripamonti, Dario
    Riva, Giulio
    Bardin, Sébastien
    van der Meiden, Hennie
    Vernimmen, Jordy
    Bystrov, Kirill
    De Temmerman, Gregory
    Interaction of adhered metallic dust with transient plasma heat loads2016In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, article id 066010Article in journal (Refereed)
    Abstract [en]

    The first study of the interaction of metallic dust (tungsten, aluminum) adhered on tungsten substrates with transient plasma heat loads is presented. Experiments were carried out in the Pilot-PSI linear device with transient heat fluxes up to 550 MW m(-2) and in the DIII-D divertor tokamak. The central role of the dust-substrate contact area in heat conduction is highlighted and confirmed by heat transfer simulations. The experiments provide evidence of the occurrence of wetting-induced coagulation, a novel growth mechanism where cluster melting accompanied by droplet wetting leads to the formation of larger grains. The physical processes behind this mechanism are elucidated. The remobilization activity of the newly formed dust and the survivability of tungsten dust on hot surfaces are documented and discussed in the light of implications for ITER.

  • 4.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shalpegin, A.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angell, M.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bardin, S.
    Brochard, F.
    Ripamonti, D.
    den Harder, N.
    De Temmerman, G.
    Elastic-plastic adhesive impacts of tungsten dust with metal surfaces in plasma environments2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 877-880Article in journal (Refereed)
    Abstract [en]

    Dust-surface collisions impose size selectivity on the ability of dust grains to migrate in scrape-off layer and divertor plasmas and to adhere to plasma-facing components. Here, we report first experimental evidence of dust impact phenomena in plasma environments concerning low-speed collisions of tungsten dust with tungsten surfaces: re-bouncing, adhesion, sliding and rolling. The results comply with the predictions of the model of elastic-perfectly plastic adhesive spheres employed in the dust dynamics code MIGRAINe for sub- to several meters per second impacts of micrometer-range metal dust.

  • 5.
    Ratynskaia, Svetlana V.
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    Weinzettl, V.
    Matejicek, J.
    Bykov, I.
    Rudakov, D. L.
    Vignitchouk, Ladislas
    KTH.
    Thorén, Emil
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Riva, G.
    Ripamonti, D.
    Morgan, T.
    Panek, R.
    De Temmerman, G.
    Tungsten dust remobilization under steady-state and transient plasma conditions2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 569-574Article in journal (Refereed)
    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.

  • 6.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Litnovsky, A.
    den Harder, N.
    Lazzaro, E.
    Migration of tungsten dust in tokamaks: role of dust-wall collisions2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 12, p. 123002-Article in journal (Refereed)
    Abstract [en]

    The modelling of a controlled tungsten dust injection experiment in TEXTOR by the dust dynamics code MIGRAINe is reported. The code, in addition to the standard dust-plasma interaction processes, also encompasses major mechanical aspects of dust-surface collisions. The use of analytical expressions for the restitution coefficients as functions of the dust radius and impact velocity allows us to account for the sticking and rebound phenomena that define which parts of the dust size distribution can migrate efficiently. The experiment provided unambiguous evidence of long-distance dust migration; artificially introduced tungsten dust particles were collected 120 degrees toroidally away from the injection point, but also a selectivity in the permissible size of transported grains was observed. The main experimental results are reproduced by modelling.

  • 7. Shalpegin, A.
    et al.
    Brochard, F.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bardin, S.
    Bystrov, K.
    Morgan, T.
    De Temmerman, G.
    Highly resolved measurements of dust motion in the sheath boundary of magnetized plasmas2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 11, article id 112001Article in journal (Refereed)
    Abstract [en]

    Dust trajectories have been recorded with an unprecedented, under fusion-relevant plasma conditions, spatial resolution of 9 mu m/pixel in Pilot-PSI. The optical setup allowed the use of fast cameras as a basic microscope. It is demonstrated that such a resolution is essential for the correct interpretation of experiments on several aspects of dust-surface interactions. Highly resolved tungsten dust dynamics measurements are presented from dedicated experiments on dust collisions with plasma facing components, motion in the vicinity of castellated samples and remobilization from planar samples.

  • 8. Shalpegin, A.
    et al.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Erofeev, I.
    Brochard, F.
    Litnovsky, A.
    Bozhenkov, S.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    den Harder, N.
    Sergienko, G.
    Fast camera observations of injected and intrinsic dust in TEXTOR2015In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 12, article id 125017Article in journal (Refereed)
    Abstract [en]

    Stereoscopic fast camera observations of pre-characterized carbon and tungsten dust injection in TEXTOR are reported, along with the modelling of tungsten particle trajectories with MIGRAINe. Particle tracking analysis of the video data showed significant differences in dust dynamics: while carbon flakes were prone to agglomeration and explosive destruction, spherical tungsten particles followed quasi-inertial trajectories. Although this inertial nature prevented any validation of the force models used in MIGRAINe, comparisons between the experimental and simulated lifetimes provide a direct evidence of dust temperature overestimation in dust dynamics codes. Furthermore, wide-view observations of the TEXTOR interior revealed the main production mechanism of intrinsic carbon dust, as well as the location of probable dust remobilization sites.

  • 9.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    De Temmerman, G.
    Ripamonti, D.
    Riva, G.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shalpegin, A.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Brochard, F.
    Bystrov, K.
    Bardin, S.
    Litnovsky, A.
    Dust remobilization in fusion plasmas under steady state conditions2016In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, no 2, article id 025009Article in journal (Refereed)
    Abstract [en]

    The first combined experimental and theoretical studies of dust remobilization by plasma forces are reported. The main theoretical aspects of remobilization in fusion devices under steady state conditions are analyzed. In particular, the dominant role of adhesive forces is highlighted and generic remobilization conditions-direct lift-up, sliding, rolling-are formulated. A novel experimental technique is proposed, based on controlled adhesion of dust grains on tungsten samples combined with detailed mapping of the dust deposition profile prior and post plasma exposure. Proof-of-principle experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are presented. The versatile environment of the linear device Pilot-PSI allowed for experiments with different magnetic field topologies and varying plasma conditions that were complemented with camera observations.

  • 10. Tolias, Panagiotis
    et al.
    Ratynskaia, Svetlana V.
    Shalpegin, A.
    Vignitchouk, Ladislas
    KTH.
    Brochard, F.
    De Angeli, M.
    van der Meiden, H.
    Experimental validation of the analytical model for tungsten dust - wall mechanical impacts incorporated in the MIGRAINe dust dynamics code2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 524-529Article in journal (Refereed)
    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.

  • 11.
    Vignitchouk, L.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ratynskaia, S.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Kantor, M.
    Ioffe Inst, St Petersburg 194021, Russia..
    Tolias, P.
    KTH Royal Inst Technol, Space & Plasma Phys, Stockholm, Sweden..
    De Angeli, M.
    CNR, Ist Fis Plasma Piero Caldirola, Via Cozzi 53, I-20125 Milan, Italy..
    van der Meiden, H.
    Dutch Inst Fundamental Energy Res, FOM Inst DIFFER, De Zaale 20, NL-5612 AJ Eindhoven, Netherlands..
    Vernimmen, J.
    Dutch Inst Fundamental Energy Res, FOM Inst DIFFER, De Zaale 20, NL-5612 AJ Eindhoven, Netherlands..
    Brochard, F.
    Univ Lorraine, Inst Jean Lamour, UMR 7198, CNRS, F-54506 Vandoeuvre Les Nancy, France..
    Shalpegin, A.
    Univ Lorraine, Inst Jean Lamour, UMR 7198, CNRS, F-54506 Vandoeuvre Les Nancy, France..
    Thorén, E.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Banon, J-P
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Validating heat balance models for tungsten dust in cold dense plasmas2018In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 11, article id 115002Article in journal (Refereed)
    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.

  • 12.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Modelling the multifaceted physics of metallic dust and droplets in fusion plasmas2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Plasma-material interaction constitutes one of the major scientific and technological issues affecting the development of thermonuclear fusion power plants. In particular, the release of metallic dust and droplets from plasmafacing components is a crucial aspect of reactor operation. By penetrating into the burning plasma, these micrometric particles act as a source of impurities which tend to radiate away the plasma energy, cooling it down below the threshold temperatures for sustainable fusion reactions. By accumulating in the reactor chamber, dust particles tend to retain fuel elements, lowering the reactor efficiency and increasing its radioactivity content. Dust accumulation also increases the risk of explosive hydrogen production upon accidental air or water ingress in the vacuum chamber. Numerical dust transport codes provide the essential framework to guide theoretical and experimental dust studies by simulating the intricate couplings between the many physical processes driving dust dynamics in fusion plasmas. This thesis reports on the development and validation of the MIGRAINe code, which specifically targets plasma-surface interaction processes and the physics of dust particles impinging on plasma-facing components to address long-term dust migration and accumulation in fusion devices.

  • 13.
    Vignitchouk, Ladislas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Delzanno, G. L.
    Los Alamos Natl Lab, Theoret Div, Los Alamos, NM 87545 USA..
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Electron reflection effects on particle and heat fluxes to positively charged dust subject to strong electron emission2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 6, article id 063702Article in journal (Refereed)
    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.

  • 14.
    Vignitchouk, Ladislas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Temmerman, Gregory
    Lehnen, Michael
    Lisgo, Steve
    Beryllium droplet cooling and distribution in the ITER vessel after a disruption2016In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326Article in journal (Refereed)
  • 15.
    Vignitchouk, Ladislas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas2017In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 10, article id 104002Article in journal (Refereed)
    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.

  • 16.
    Vignitchouk, Ladislas
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Dust-wall and dust-plasma interaction in the MIGRAINe code2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 9, p. 095005-Article in journal (Refereed)
    Abstract [en]

    The physical models implemented in the recently developed dust dynamics code MIGRAINe are described. A major update of the treatment of secondary electron emission, stemming from models adapted to typical scrape-off layer temperatures, is reported. Sputtering and plasma species backscattering are introduced from fits of available experimental data and their relative importance to dust charging and heating is assessed in fusion-relevant scenarios. Moreover, the description of collisions between dust particles and plasma-facing components, based on the approximation of elastic-perfectly plastic adhesive spheres, has been upgraded to take into account the effects of particle size and temperature.

1 - 16 of 16
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