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  • 1. Annibaldi, S. V.
    et al.
    Ivlev, A. V.
    Konopka, U.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Thomas, H. M.
    Morfill, G. E.
    Lipaev, A. M.
    Molotkov, V. I.
    Petrov, O. F.
    Fortov, V. E.
    Dust-acoustic dispersion relation in three-dimensional complex plasmas under microgravity2007Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of dedicated experiments with the Plasma Kristal Experiment ( PKE)-Nefedov ( Nefedov et al 2003 New J. Phys. 5 33) set-up were performed on board the International Space Station to measure the dispersion relation ( DR) for the longitudinal dust-acoustic ( DA) waves in quasi-isotropic three-dimensional ( 3D) complex plasmas. The waves were excited by applying ac electric modulation of variable frequency to the radio frequency ( rf) electrodes. The amplitude of excitation was varied with frequency to ensure a 'sufficiently linear' regime of the dust density perturbations. The DR was obtained by measuring the induced density perturbations, revealing fairly good agreement with a simple multispecies theory of DA waves.

  • 2.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Litnovsky, A.
    Ogata, Douglas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sahle, Wubeshet
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Studies of mobile dust in scrape-off layer plasmas using silica aerogel collectors2011Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, nr 1, s. S1089-S1093Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dust capture with ultralow density silica aerogel collectors is a new method, which allows time resolved in situ capture of dust particles in the scrape-off layers of fusion devices, without substantially damaging the particles. Particle composition and morphology, particle flux densities and particle velocity distributions can be determined through appropriate analysis of the aerogel surfaces after exposure. The method has been applied in comparative studies of intrinsic dust in the TEXTOR tokamak and in the Extrap T2R reversed field pinch. The analysis methods have been mainly optical microscopy and SEM. The method is shown to be applicable in both devices and the results are tentatively compared between the two plasma devices, which are very different in terms of edge plasma conditions, time scale, geometry and wall materials.

  • 3. Bykov, I.
    et al.
    Rudakov, D. L.
    Ratynskaia, Svetlana V.
    Tolias, Panagiotis
    De Angeli, M.
    Hollmann, E. M.
    McLean, A. G.
    Lasnier, C. J.
    Riva, G.
    Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 379-385Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ogata, Douglas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Collection of mobile dust in the T2R reversed field pinch2012Ingår i: Nukleonika, ISSN 0029-5922, E-ISSN 1508-5791, Vol. 57, nr 1, s. 55-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intensive plasma-wall interactions in fusion devices result in the impurity production and the formation of films of redeposited material, debris and dust. In present day devices, with short pulses, the mobile dust does not pose any serious operational problems, but it is a matter of serious concern for ITER and for later power producing devices with a high duty cycle. We report results of a dust collection experiment carried out at the T2R reversed field pinch device and related heavy impurity flux measurements. Dust and impurities were collected on passive Si surface probes and on ultralow density silica aerogel collectors. The advantage of the latter method is the possibility of nondestructive capture of the micron- and submicron-sized dust particles. The toroidal and radial deposition fluxes of dust particles and impurities are estimated and discussed in the light of the dominant forces acting on the dust.

  • 5.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Litnovsky, A.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer2013Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S681-S685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Moving dust has been collected in the SOL of TEXTOR in a time-resolved way with silica aerogel collectors [1-3]. The collectors were exposed to the toroidal particle flux in NBI heated discharges during the startup and flat top phase. Intrinsic dust was collected in several discharges. Other discharges were accompanied with injection of known amounts of pre-characterized dust (W, C flakes and C microspheres) from a position toroidally 120° away from the collector. Particle flux, composition and dust size distribution have been determined with SEM and EDX. Calibration allowed particle velocity estimates to be made. Upper limits for the deuterium content of individual dust grains have been determined by NRA.

  • 6.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Banon, Jean-Philippe
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration2014Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, nr 3, s. 035014-Artikel i tidskrift (Refereegranskat)
    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.

  • 7. Castaldo, C.
    et al.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    De Angeli, M.
    de Angelis, U.
    On the feasibility of electro-optical detection of dust-impact ionization in tokamaks2010Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, nr 10, s. 105003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The feasibility of the optical and electrical detection of dust-impact ionization events in the scrape-off layers of tokamak plasmas is evaluated. It is shown that the expected light emission and the charge released during a dust impact on a biased target can be measured above the light emission and the charge collected due to the background plasma. A scheme of an electro-optical probe for diagnostics of fast dust particles is proposed.

  • 8. Castaldo, C.
    et al.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Pericoli, V.
    Rypdal, K.
    De Angelis, U.
    Morfill, G. E.
    Pieroni, L.
    Capobianco, G.
    De Angeli, M.
    Gabellieri, L.
    Giovannozzi, E.
    Maddaluno, G.
    Marmolino, C.
    Orsitto, F.
    Romano, A.
    Rufoloni, A.
    Tuccillo, A. A.
    Fast dust particles in tokamak plasmas: Detection and effects2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, nr 2, s. 848-851Konferensbidrag (Refereegranskat)
  • 9. Castaldo, C.
    et al.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Pericoli, V.
    de Angelis, U.
    Rypdal, K.
    Pieroni, L.
    Giovannozzi, E.
    Maddaluno, G.
    Marmolino, C.
    Rufoloni, A.
    Tuccillo, A.
    Kretschmer, M.
    Morfill, G. E.
    Diagnostics of fast dust particles in tokamak edge plasmas2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 7, s. L5-L9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of the Frascati Tokamak Upgrade revealed that some features of the signals can be explained only by a local non-propagating phenomenon. These signal features are shown to be both in qualitative and quantitative agreement with ionization, and consequent extra charge collected by the probes, due to the impact of micrometre-sized dust at a velocity of the order of 10 km s(- 1). Electron microscope analysis of the probe surface yielded direct support for such an interpretation.

  • 10. De Angeli, M.
    et al.
    Castaldo, C.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Grosso, G.
    Almaviva, S.
    Caneve, L.
    Colao, F.
    Maddaluno, G.
    Note: Simultaneous electrical and optical detection of expanding dense partially ionized vapour clouds2011Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, nr 10, s. 106101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The scheme and construction of an electro-optical probe able to collect charge and detect optical emission from expanding dense partially ionized vapour clouds are reported. The instrument can be applied to phenomena such as dust impact ionization and solid target laser ablation. First, results of measurements of expanding plasma cloud formed upon ablating W target are presented. Use of the instrument in different experimental facilities, including tokamak, is discussed.

  • 11. De Angeli, M.
    et al.
    Tolias, Panagiotis
    Ratynskaia, Svetlana V.
    Ripamonti, D.
    Riva, G.
    Bardin, S.
    Morgan, T.
    De Temmerman, G.
    Remobilization of tungsten dust from castellated plasma-facing components2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 536-540Artikel i tidskrift (Refereegranskat)
    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.

  • 12. de Angelis, U.
    et al.
    Regnoli, G.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Long-range attraction of negatively charged dust particles in weakly ionized dense dust clouds2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 4, s. 043702-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The new Plasma Kristall Experiment (PK-4) is scheduled to fly on the International Space Station in 2012 with one of the experiments designed to investigate the existence of two fluid phases and a critical point in complex plasmas. A crucial issue is the parameter regime where the critical point could be found and this requires, as a first step, knowledge of the parameter range where dust-dust attraction can exist. This problem is addressed in the present work, extending previous works on long-range screening and attraction of negatively charged dust particles in plasmas. The roles of nonlinearities, ion-neutral collisions, electron dynamics, and plasma source on the depth and long-range behavior of the attractive well are established and the impact of these results on the PK-4 experiments is discussed.

  • 13. de Angelis, Umberto
    et al.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Effects of dust particles in plasma kinetics; ion dynamics time scales2012Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, nr 7, s. 073701-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The self-consistent kinetic theory of dusty plasmas [V. N. Tsytovich and U. de Angelis, Phys. Plasmas 6, 1093 (1999)] is extended to frequency regimes relevant for ion dynamics, accounting for both constant and fluctuating plasma sources. In contrast to earlier models, binary plasma collisions are no longer neglected with respect to collisions with dust; hence, the model developed here is also valid for low dust densities. Expressions are found for the system's permittivity, the ion collision integral, and the spectral densities of ion density fluctuations. The structure of the ion kinetic equation is analyzed, and applications of the model for both astrophysical and laboratory environments are discussed.

  • 14. Demidov, V. I.
    et al.
    Ratynskaia, Svetlana V.
    Rypdal, K.
    Electric probes for plasmas: The link between theory and instrument2002Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 73, nr 10, s. 3409-3439Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Electric probe methods for diagnostics of plasmas are reviewed with emphasis on the link between the appropriate probe theories and the instrumental design. The starting point is an elementary discussion of the working principles and a discussion of the physical quantities that can be measured by the probe method. This is followed by a systematic classification of the various regimes of probe operation and a summary of theories and methods for measurements of charged particle distributions. Application of a single probe and probe clusters for measurements of fluid observables is discussed. Probe clusters permit both instantaneous and time-averaged measurements without sweeping the probe voltage. Two classes of applications are presented as illustrations of the methods reviewed. These are measurements of cross sections and collision frequencies (plasma electron spectroscopy), and measurements of fluctuations and anomalous transport in magnetized plasma.

  • 15. Demidov, V. I.
    et al.
    Ratynskaia, Svetlana V.
    Rypdal, K.
    Reducing influence of ion current on measurements of electron energy distributions in collisional plasmas2001Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 72, nr 11, s. 4106-4109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method for reducing the influence of ion current on probe measurements of electron velocity distributions in plasmas has been developed and tested in noble gas afterglow plasmas. It is valid for diffusive transport of ions to the probe. Experiments have demonstrated high accuracy of the proposed method.

  • 16. Demidov, V. I.
    et al.
    Ratynskaia, Svetlana V.
    Rypdal, K.
    The analysis of probe I-V characteristics in a magnetized low-temperature plasma2001Ingår i: Contributions to Plasma Physics, ISSN 0863-1042, E-ISSN 1521-3986, Vol. 41, nr 5, s. 443-448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The validity of probe theories based on the classical electron transport to probes in low-temperature magnetized plasma of the toroidal device `Blaamann has been demonstrated. The analysis was carried out for the conditions when global transport of charged particles in the device is anomalous, namely for magnetic field up to 0.3 T and pressure range 0.1 - 1 Pa. It was shown also that for the magnetic field larger than 0.1 T probes longer than 15 mm provide electron saturation current practically independent of probe potential, hence more accurate measurements of the plasma parameters. The experiments have revealed that application of long probes oriented parallel to the magnetic field may cause an anomaly of the I-V characteristics in the sense that a local increase of the electron current appears near the plasma potential.

  • 17. Fortov, V.
    et al.
    Morfill, G.
    Petrov, O.
    Thoma, M.
    Usachev, A.
    Hoefner, H.
    Zobnin, A.
    Kretschmer, M.
    Ratynskaia, Svetlana V.
    Fink, M.
    Tarantik, K.
    Gerasimov, Y.
    Esenkov, V.
    The project 'Plasmakristall-4' (PK-4) - a new stage in investigations of dusty plasmas under microgravity conditions: first results and future plans2005Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, s. B537-B549Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The PK-4 experiment is a continuation of the successful dusty plasma experiments PK-1, PK-2 and PK-3 conducted on board of the orbital space stations Mir and International Space Station. For all these experiments it is important to avoid the strong influence of gravity, exerting an external stress on the system. Whereas PK-3 and PK-3 Plus experiments are using a planar rf capacitive discharge, PK-4 studies complex plasmas in a long cylindrical chamber with a combined dc/rf discharge. Such a configuration of the chamber will provide a particular advantage for investigation of different dynamical phenomena in complex plasmas such as sheared laminar flow of a highly nonideal dusty liquid and its transition to the turbulent regime, nozzle flow, boundary layers and instabilities, shock waves (solitons) formation and propagation, dust particle lane formation, and space dust grain separation according to their size.

  • 18. Giovannozzi, E.
    et al.
    Castaldo, C.
    Apruzzese, G.
    Maddaluno, G.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rydzy, A.
    Dust in FTU with the Thomson scattering diagnostic2008Ingår i: AIP CONF PROC, 2008, Vol. 1041, s. 213-214Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Thomson scattering diagnostic has been used to measure the dust present in plasma discharges on FTU tokamak after disruption. The vaporization of the dust particles due to die high power of the laser used by the Thomson scattering diagnostic imply that only a rough estimate of the particle size could be derived from the elastic scattering of the laser light. A simple model for dust particle evaporation has been used to infer the size of the dust particle from the scattered light data.

  • 19. Giovannozzi, E.
    et al.
    Castaldo, C.
    Maddaluno, G.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rydzy, A.
    Dust measurement with Thomson scattering in FTU2008Ingår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 988, s. 148-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The size distribution of dust particles present in FTU after disruptions has been evaluated in the range 0.05 mu m - 0.1 mu m using the Thomson scattering system. Rayleigh approximation has been used to estimate the dust size. The distribution, although the radii considered do not differ more than an order of magnitude, behave like a power law. The laser energy density far exceed that necessary to vaporize, at least partially, the particles. This can affect the previous estimate of the particle sizes, and suggests that the effective radii might be larger than the estimated values. A preliminary analysis on the broad band signal is presented.

  • 20. Kantor, M.
    et al.
    Tsalas, M.
    Litnovsky, A.
    Rudakov, D.
    Bozhenkov, S.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ashikawa, N.
    Pospieszczyk, A.
    Philipps, V.
    Characterization of dust particles in the TEXTOR tokamak with Thomson scattering diagnostic2013Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S711-S714Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The presence of dust particles in a fusion plasma is recognized as a serious issue for safe and efficient operation of the ITER tokamak. The paper presents an in situ laser assisted method for characterization of dust from thermal emission of the particles. The method was developed in the TEXTOR tokamak with the use of Thomson scattering (TS). The diagnostic is capable to detect single particles and measure the dust density profile along the laser probing axis, velocity distribution of dust particles along this axis as well as surface temperature and size of the detected particles.

  • 21. Khrapak, S. A.
    et al.
    Ratynskaia, Svetlana V.
    Zobnin, A. V.
    Usachev, A. D.
    Yaroshenko, V. V.
    Thoma, M. H.
    Kretschmer, M.
    Hofner, H.
    Morfill, G. E.
    Petrov, O. F.
    Fortov, V. E.
    Particle charge in the bulk of gas discharges2005Ingår i: Physical Review E, ISSN 1539-3755, Vol. 72, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental determination of particle charge in a bulk dc discharge plasma covering a wide range of neutral gas pressures, was recently reported [S. Ratynskaia , Phys. Rev. Lett. 93, 085001 (2004)]. The charges obtained were several times smaller than the predictions of collisionless orbital motion limited theory. This discrepancy was attributed to the effect of ion-neutral collisions. In the present paper a more detailed description of this experiment is provided and additional experimental results obtained with particles of different sizes are reported. The measurements are compared with molecular dynamics simulations of particle charging for conditions similar to those of the experiment, with other available experimental data on particle charge in the bulk of gas discharges, and with a simple analytical model accounting for ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent a very important factor, which significantly affects (reduces) the particle charge under typical discharge conditions.

  • 22. Khrapak, S. A.
    et al.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Chaudhuri, M.
    Zobnin, A.
    Usachev, A.
    Rau, C.
    Thoma, M. H.
    Petrov, O. F.
    Fortov, V. E.
    Morfill, G. E.
    Grain charging in an intermediately collisional plasma2012Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, nr 3, s. 35001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The charges of mu m-size particles in the quasineutral bulk plasma of a dc discharge are determined experimentally in a pressure range between 100 and 500 Pa, spanning the transition between the weakly collisional and highly collisional (hydrodynamic) regimes, where the ion mean free path drops below the plasma screening length. The charge is determined using the force balance condition from the measured particle drift velocities in stable particle flows. A simple interpolation formula for the ion flux to the grain in the transitional regime is shown to fit quite well the experimental results.

  • 23. Komm, M.
    et al.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Cavalier, J.
    Dejarnac, R.
    Gunn, J. P.
    Podolnik, A.
    On thermionic emission from plasma-facing components in tokamak-relevant conditions2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 9, artikel-id 094002Artikel i tidskrift (Refereegranskat)
    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.

  • 24. Komm, M.
    et al.
    Tolias, Panagiotis
    Ratynskaia, Svetlana V.
    Dejarnac, R.
    Gunn, J. P.
    Krieger, K.
    Podolnik, A.
    Pitts, R. A.
    Panek, R.
    Simulations of thermionic suppression during tungsten transient melting experiments2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 014069Artikel i tidskrift (Refereegranskat)
    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.

  • 25. Krieger, K.
    et al.
    Sieglin, B.
    Balden, M.
    Coenen, J. W.
    Goeths, B.
    Laggner, F.
    de Marne, P.
    Matthews, G. F.
    Nille, D.
    Rohde, V.
    Dejarnac, R.
    Faitsch, M.
    Giannone, L.
    Herrmann, A.
    Horacek, J.
    Komm, M.
    Pitts, R. A.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Thorén, E.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tolias, P.
    Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 014030Artikel i tidskrift (Refereegranskat)
    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.

  • 26.
    Labit, B.
    et al.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Thorén, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Vallejos Olivares, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 8, artikel-id 086020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (n(e,sep)/n(G) similar to 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.

  • 27. Laguardia, L.
    et al.
    Cremona, A.
    De Angeli, M.
    Lazzaro, E.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Passoni, M.
    Dellasega, D.
    Gervasini, G.
    Grosso, G.
    Schiavone, R.
    Vassallo, E.
    Formation of dust in low-pressure magnetized hydrocarbon plasmas2011Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, s. 063006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapid formation of large molecules and the subsequent production of solid-state dust particles in a low-pressure discharge is unlikely, because of the low rates of the polymerization reactions and short lifetimes of the species. Here, we suggest that C dust particles can form in atypically low (10(-3) mbar)-pressure hydrocarbon plasmas if the dust charging time is much shorter than the gas residence time in the device; we present supporting experimental evidence for this. Such a condition can be obtained by the production of high-density plasmas. The results show that dust formation from the gaseous phase can occur in a much wider parameter range than is commonly assumed.

  • 28. Lazzaro, E.
    et al.
    Proverbio, I.
    Nespoli, F.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    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 vessel2012Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, nr 12, s. 124043-Artikel i tidskrift (Refereegranskat)
    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.

  • 29. Lazzaro, E.
    et al.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Proverbio, I.
    Hypervelocity regime of dust particles in tokamaks2011Ingår i: AIP Conf. Proc., 2011, s. 103-109Konferensbidrag (Refereegranskat)
    Abstract [en]

    The mobilization and acceleration of metallic dust in gap region between the last closed confinement surface and the vessel wall of the Frascati Tokamak Upgrade (FTU) is studied numerically for the definition of appropriate location of diagnostics devoted to dust dynamics.

  • 30. Litnovsky, A.
    et al.
    Rudakov, D. L.
    Bozhenkov, S.
    Smirnov, R. D.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ashikawa, N.
    De Temmerman, G.
    Xu, Y.
    Krasheninnikov, S. I.
    Biel, W.
    Brezinsek, S.
    Coenen, J. W.
    Kreter, A.
    Kantor, M.
    Lambertz, H. T.
    Philipps, V.
    Pospieszczyk, A.
    Samm, U.
    Sergienko, G.
    Schmitz, O.
    Stoschus, H.
    Dust investigations in TEXTOR: Impact of dust on plasma-wall interactions and on plasma performance2013Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S126-S132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dust will have severe impact on ITER performance since the accumulation of tritium in dust represents a safety issue, a possible reaction of dust with air and steam imposes an explosion hazard and the penetration of dust in core plasmas may degrade plasma performance by increasing radiative losses. Investigations were performed in TEXTOR where known amounts of pre-characterized carbon, diamond and tungsten dust were mobilized into plasmas using special dust holders. Mobilization of dust changed a balance between plasma-surface interactions processes, significantly increasing net deposition. Immediately after launch dust was dominating both core and edge plasma parameters. Remarkably, in about 100 ms after the launch, the effect of dust on edge and core plasma parameters was vanished: no increase of carbon and tungsten concentrations in the core plasmas was detected suggesting a prompt transport of dust to the nearby plasma-facing components without further residence in the plasma.

  • 31. Nespoli, F.
    et al.
    Lazzaro, E.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Proverbio, I.
    De Angeli, M.
    Castaldo, C.
    De Angelis, U.
    Grosso, G.
    Modelling and diagnostics of hypervelocity dust particles in a tokamak2012Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 1., 2012, s. 520-523Konferensbidrag (Refereegranskat)
  • 32.
    Olson, Jonas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Miloch, W.J.
    Department of Physics and Technology, University of Tromsö, Norway.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Yaroshenko, V.
    Max-Planck-Institute für Extraterrestrische Physik, Germany.
    Potential structure around th Cassini spacecraft near the orbit of Enceladus2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of numerical simulations of the potential structure around an object in a streaming plasma with parameters relevant for the Cassini spacecraft passing through Saturn's plasma disk near the orbit of Enceladus. Two-and three-dimensional particle-in-cell codes have been used allowing the potential of the simulated spacecraft body to develop self-consistently through the collection of charge by its surface. The dependence of the density and potential profiles on ambient plasma density, electron temperature, and ion drift speed is discussed. The spacecraft floating potential values, found in the simulations, are compared to those deduced from the analysis of Cassini Langmuir probe characteristics.

  • 33.
    Panarese, A.
    et al.
    Univ Bari, Dept Chem, I-70126 Bari, Italy.;CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    Bruno, D.
    CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. st Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy..
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Longo, S.
    Univ Bari, Dept Chem, I-70126 Bari, Italy.;CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    de Angelis, U.
    Ist Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy..
    Molecular dynamics calculation of the spectral densities of plasma fluctuations2018Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, nr 3, artikel-id 905840308Artikel i tidskrift (Refereegranskat)
    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.

  • 34. Proverbio, I.
    et al.
    Lazzaro, E.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Castaldo, C.
    De Angelis, U.
    Grosso, G.
    De Angeli, M.
    The dynamics of ferromagnetic dust particles in the FTU tokamak2011Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, nr 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mobilization and acceleration of metallic dust in the gap region between the last closed confinement surface and the vessel wall of the Frascati Tokamak Upgrade (FTU) is studied numerically for the definition of the appropriate location of diagnostics devoted to dust dynamics.

  • 35.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dusty plasmas vs. multicomponent plasmas2012Ingår i: Nukleonika, ISSN 0029-5922, E-ISSN 1508-5791, Vol. 57, nr 2, s. 307-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different approaches employed for dusty plasmas, ranging from single particle description (valid for low dust densities) to models appropriate in the presence of dense dusty clouds, are briefly reviewed. For environments with high dust density, a selection of examples is provided to elucidate phenomena arising in dusty plasmas when the effects of absorption of plasma particles on the dust surfaces and dust charge fluctuations are of importance and cannot be neglected.

  • 36.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Castaldo, C.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rudakov, D.
    Diagnostics of mobile dust in scrape-off layer plasmas2011Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, nr 7, s. 074009-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dust production and accumulation pose serious safety and operational implications for the next generation fusion devices. Mobile dust particles can result in core plasma contamination with impurities, and those with high velocities can significantly contribute to the wall erosion. Diagnostics for monitoring dust in tokamaks during plasma discharges are hence important as they can provide information on dust velocity and size, and-in some cases-on dust composition. Such measurements are also valuable as an input for theoretical models of dust dynamics in scrape-off layer plasmas. Existing in situ dust diagnostics, focusing on the range of dust parameters they can detect, are reviewed. Particular attention is paid to the diagnostics which allow us to detect tails of the dust velocity and size distributions, e.g. small and very fast particles. Some of the techniques discussed have been adopted from space-related research and have been shown to be feasible and useful for tokamak applications as well.

  • 37.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dilecce, G.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    BABE - a brush cathode discharge for thermal fluctuation measurements2015Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, artikel-id 345810202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For experimental tests of fluctuation theory in ideal plasmas and plasmas seeded with dust, the ideal environment would be that of stable quiescent plasma. In most laboratory plasmas the homogeneous state of the positive column is often unstable, rare exceptions are the so-called brush cathode discharges, proposed in the 60s, where a specially manufactured cathode allows stable operation in the abnormal glow regime and the only fluctuations present are those due the thermal motion of the particles. Such a device, the BAri Brush Electrode (BABE), has recently been built in a novel configuration that combines the advantages of the inverse design with those of the reflex geometry. The region between the two anodes is essentially field-free and extremely stable in wide range of plasma densities and collisionalities. Unprecedented low fluctuation levels of delta n/n <= 10(-5) in He and delta n/n <= 5 x 10(-6) in Ar discharges have been achieved.

  • 38.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dilecce, G.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Nitrogen optical emission during nanosecond laser ablation of metals: prompt electrons or photo-ionization?2014Ingår i: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 117, nr 1, s. 409-413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments on the interaction of metal targets with a Nd:YAG laser beam ( = 1,064 nm, intensity -) are carried out in a finite Nitrogen pressure environment. The observed spectra are unambiguous evidence of the existence of an ionization and excitation source, arriving at the observation volume prior to the plume. Such a source can be either prompt electrons or VUV radiation. The analysis reveals that the prompt electron interpretation requires energies in excess of 1 keV, incompatible with any acceleration mechanisms relevant for such laser intensities. On the other hand, VUV radiation is sufficiently strong to explain the observed spectra.

  • 39.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Jacquemot, Sylvie
    41st European Physical Society Conference on Plasma Physics Preface2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 1, s. 010301-Artikel i tidskrift (Refereegranskat)
  • 40.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Regnoli, Giorgio
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Klumov, B.
    Rypdal, K.
    Grain transport in three-dimensional soft dusty plasma states2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 3, s. 034502-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three-dimensional molecular dynamics simulations of aggregates of dust grains interacting via repulsive Yukawa forces, and subject to heating by neutrals and realistic boundary conditions, suggest that grain transport is ubiquitously anomalous for soft states at the transition between liquid and solid. These anomalies include self-similar, stretched-Gaussian, probability density distributions of grain displacements and superdiffusive displacement scaling on the short time scales for which the mean displacements sigma(tau) are less than the interparticle distance Delta. However, the details of the anomalous transport on these shorter time scales depend on system stiffness and confinement conditions. On time scales for which sigma(tau) >= Delta, humps can develop on the distribution at integer multiples of Delta, an effect of cooperative hopping of grains on the lattice. Relaxation toward Gaussian displacement distributions and normal diffusion takes place on time scales for which sigma(tau) > Delta. The simulations indicate that qualitative features previously found for hexatic states of two-dimensional aggregates by simulation and experiment are also present in three-dimensional configurations. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3334377]

  • 41.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bykov, Igor
    Rudakov, Dmitry
    De Angeli, Marco
    Vignitchouk, Ladislas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    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 loads2016Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, artikel-id 066010Artikel i tidskrift (Refereegranskat)
    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.

  • 42.
    Ratynskaia, Svetlana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Shalpegin, A.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    De Angell, M.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bardin, S.
    Brochard, F.
    Ripamonti, D.
    den Harder, N.
    De Temmerman, G.
    Elastic-plastic adhesive impacts of tungsten dust with metal surfaces in plasma environments2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 877-880Artikel i tidskrift (Refereegranskat)
    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.

  • 43.
    Ratynskaia, Svetlana V.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Litnovsky, A.
    Kreter, A.
    Philipps, V.
    Capture by aerogel-characterization of mobile dust in tokamak scrape-off layer plasmas2009Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, nr 12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this letter is to demonstrate the feasibility and potential of the novel in situ dust diagnostic method-capture by aerogel targets. Aerogel, a highly porous material with a density of a few tens of kg m(-3), allows capturing of dust particles present during the discharge without destroying them. The first exposures in the TEXTOR scrape-off layer plasma showed that such targets are able to capture both slow and fast particles with sizes in the range from submicrometre to similar to 100 mu m. The technique provides information on dust velocity and size distribution as well as dust flux estimates. The composition and texture of the captured dust can also be studied in detail to shed light on dust formation processes.

  • 44.
    Ratynskaia, Svetlana V.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Castaldo, C.
    Giovannozzi, E.
    Rudakov, D.
    Morfill, G.
    Horanyi, M.
    Yu, J. H.
    Maddaluno, G.
    In situ dust detection in fusion devices2008Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, nr 12, s. 124046-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diagnostics for monitoring dust in tokamaks during plasma discharges, both established and currently being developed, are discussed with a focus on the range of dust parameters they can detect. Visible imaging can currently be used for dust particles bigger than a few mu m and velocities below 1 km s(-1). The dust impact ionization phenomenon can be used for the detection of particles with velocities above a few km s(-1). Laser light scattering gives an insight into the amount of sub-micron dust. Aerogels, light porous materials, allow capturing of dust particles without destroying them and determining their velocity. Other methods include the microbalance technique and electrostatic dust detectors. A recent suggestion to use the effects of dust on collective scattering for diagnostic purposes is also discussed.

  • 45.
    Ratynskaia, Svetlana V.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Castaldo, C.
    Rypdal, K.
    Morfill, G.
    de Angelis, U.
    Pericoli-Ridolfini, V.
    Rufoloni, A.
    Giovannozzi, E.
    Hypervelocity dust impacts in FTU scrape-off layer2008Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 48, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first evidence of dust-impact ionization processes in the scrape-off layer of the Frascati tokamak upgrade (FTU) was reported in Nucl. Fusion 47 L5 (2007). In this work an extended data analysis (both of electrostatic probe signals and probe surface analysis) is presented, using results of empirical studies of hypervelocity impacts. Within the accuracy and limits of application of such results to tokamak plasma environment, the data are shown to be consistent with occurrence of impacts by micrometre size iron particles at velocities of the order of 10 km s(-1).

  • 46.
    Ratynskaia, Svetlana V.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    De Angeli, M.
    de Angelis, U.
    Marmolino, C.
    Capobianco, G.
    Lontano, M.
    Lazzaro, E.
    Morfill, G. E.
    Gervasini, G.
    Observation of the effects of dust particles on plasma fluctuation spectra2007Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, nr 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Charged dust particles are theoretically expected to modify the amplitude and spectrum of plasma fluctuations, and this can eventually provide novel diagnostic tools. Direct experimental evidence of the effects of dust particles on the fluctuations of a low collisionality plasma is reported, in agreement with the expectations of kinetic theory.

  • 47. Ratynskaia, Svetlana V.
    et al.
    de Angelis, U.
    Khrapak, S.
    Klumov, B.
    Morfill, G. E.
    Electrostatic interaction between dust particles in weakly ionized complex plasmas2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electrostatic potential around a dust particle in a complex plasma is calculated, taking into account ion-neutral collisions and collective effects, in a range of plasma parameters relevant for typical laboratory experiments. The existence of attractive wells and dependence of their shape on the main experimental control parameters, neutral gas pressure, and dust number density, is investigated.

  • 48. Ratynskaia, Svetlana V.
    et al.
    Demidov, V. I.
    Rypdal, K.
    A probe for measurements of electrostatic fluctuations in a low-temperature magnetized plasma2000Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 71, nr 3, s. 1367-1369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A cylindrical probe with insulating end plugs for investigations of fluctuations of electron temperature and plasma potential is proposed. The radii of the metallic rod and plugs are chosen to optimize the ratio of ion saturation current to electron saturation current (> 1) for the probe oriented parallel to the magnetic field. This probe is applicable when the electron temperature is much larger than the ion temperature.

  • 49. Ratynskaia, Svetlana V.
    et al.
    Demidov, V. I.
    Rypdal, K.
    Measurements of anomalous particle and energy fluxes in a magnetized plasma2002Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 65, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrostatic probe measurements of low frequency plasma fluctuations and anomalous particle and energy flux densities in a magnetized plasma are presented. A method allowing the simultaneous recording of instantaneous electric field, electron density, and temperature is invoked. The method is applied to flux density measurements in a weakly ionized, low beta plasma created in a toroidal device without magnetic rotational transform. It is also used to identify modes belonging to different dispersion branches and to obtain the dispersion relations for these modes. For the plasma states studied, the phase velocities and the cross phase between the electron density and electric field agree with those predicted from a local, linear stability analysis for electrostatic flute modes and drift waves. The instability threshold, however, is one order of magnitude higher than predicted by theory for unsheared flow. The fluxes measured are consistent with the estimated ionization rate.

  • 50. Ratynskaia, Svetlana V.
    et al.
    Demidov, V. I.
    Rypdal, K.
    Probe measurements of electron temperature and density in strongly magnetized plasma2000Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 71, nr 9, s. 3382-3384Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It was demonstrated that with increasing probe length the electron saturation current becomes more independent of the probe potential. This provides higher accuracy of measurements of the electron density and plasma potential in a strongly magnetized plasma (B > 0.1 T). Long probes oriented parallel to the magnetic field yield better spatial resolution in the perpendicular direction. Parallel probes, however, are very sensitive to alignment errors. To avoid this problem, a cylindrical probe with a side surface coated by a thin insulating layer is proposed.

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