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  • 1.
    Blanken, T. C.
    et al.
    Eindhoven Univ Technol, Control Syst Technol Grp, Dept Mech Engn, POB 513, NL-5600 MB Eindhoven, Netherlands.;Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Fridström, Richard
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, T.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Dori, V
    Univ Split, Fac Elect Engn Mech Engn & Naval Architecture, R Boskovica 32, Split 21000, Croatia..
    Real-time plasma state monitoring and supervisory control on TCV2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 2, article id 026017Article in journal (Refereed)
    Abstract [en]

    In ITER and DEMO, various control objectives related to plasma control must be simultaneously achieved by the plasma control system (PCS), in both normal operation as well as off-normal conditions. The PCS must act on off-normal events and deviations from the target scenario, since certain sequences (chains) of events can precede disruptions. It is important that these decisions are made while maintaining a coherent prioritization between the real-time control tasks to ensure high-performance operation. In this paper, a generic architecture for task-based integrated plasma control is proposed. The architecture is characterized by the separation of state estimation, event detection, decisions and task execution among different algorithms, with standardized signal interfaces. Central to the architecture are a plasma state monitor and supervisory controller. In the plasma state monitor, discrete events in the continuous-valued plasma state arc modeled using finite state machines. This provides a high-level representation of the plasma state. The supervisory controller coordinates the execution of multiple plasma control tasks by assigning task priorities, based on the finite states of the plasma and the pulse schedule. These algorithms were implemented on the TCV digital control system and integrated with actuator resource management and existing state estimation algorithms and controllers. The plasma state monitor on TCV can track a multitude of plasma events, related to plasma current, rotating and locked neoclassical tearing modes, and position displacements. In TCV experiments on simultaneous control of plasma pressure, safety factor profile and NTMs using electron cyclotron heating (ECI I) and current drive (ECCD), the supervisory controller assigns priorities to the relevant control tasks. The tasks are then executed by feedback controllers and actuator allocation management. This work forms a significant step forward in the ongoing integration of control capabilities in experiments on TCV, in support of tokamak reactor operation.

  • 2. Brezinsek, S.
    et al.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zaplotnik, R.
    et al.,
    Plasma-wall interaction studies within the EUROfusion consortium: Progress on plasma-facing components development and qualification2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 11, article id 116041Article in journal (Refereed)
    Abstract [en]

    The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.

  • 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-D2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 379-385Article in journal (Refereed)
    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, 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.

  • 5.
    Causa, F.
    et al.
    CNR, Ist Fis Plasma Piero Caldirola, Via R Cozzi 53, I-20125 Milan, Italy.;CNR, Ist Fis Plasma, Via R Cozzi 53, I-20125 Milan, Italy..
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Zito, P.
    ENEA, Fus & Nucl Safety Dept, CR Frascati, Via E Fermi 45, I-00044 Rome, Italy..
    Analysis of runaway electron expulsion during tokamak instabilities detected by a single-channel Cherenkov probe in FTU2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 4, article id 046013Article in journal (Refereed)
    Abstract [en]

    The expulsion of runaway electrons (REs) during different types of tokamak instabilities is analysed by means of a Cherenkov probe inserted into the scrape-off layer of the FTU tokamak. One such type of instability, the well-known tearing mode, is involved in disruptive plasma termination events, during which the risk of RE avalanche multiplication is highest. The second type, known as anomalous Doppler instability, influences RE dynamics by enhancing pitch angle scattering. Three scenarios are analysed here, characterised by different RE generation rates and mechanisms. The main conclusions are drawn from correlations between the Cherenkov probe and other diagnostics. In particular, the Cherenkov probe permits the detection of fast electron expulsion with a high level of detail, presenting peaks with 100% signal contrast during tearing mode growth and rotation, and sub-peak structures reflecting the interplay between the magnetic island formed by the tearing mode, RE diffusion during island rotation and the geometry of obstacles in the vessel. Correlations between the Cherenkov signal, hard x-ray emission and electron cyclotron emission reveal the impulsive development of the anomalous Doppler instability with instability rise time in the microsecond scale resolved by the high time-resolution of the Cherenkov probe.

  • 6.
    De Angeli, M.
    et al.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Lazzaro, E.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    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.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Castaldo, C.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Apicella, M. L.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Gervasini, G.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Giacomi, G.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Giovannozzi, E.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Granucci, G.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Iafrati, M.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Iraji, D.
    Amirkabir Univ Technol, Energy Engn & Phys Dept, Tehran, Iran..
    Maddaluno, G.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Riva, G.
    CNR, Ist Chim Mat Condensata & Tecnol Energia, Via R Cozzi 53, I-20125 Milan, Italy..
    Uccello, A.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Pre-plasma remobilization of ferromagnetic dust in FTU and possible interference with tokamak operations2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 10, article id 106033Article in journal (Refereed)
    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.

  • 7. 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 components2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 536-540Article in journal (Refereed)
    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.

  • 8. de Angelis, Umberto
    et al.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Effects of dust particles in plasma kinetics; ion dynamics time scales2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 7, p. 073701-Article in journal (Refereed)
    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.

  • 9.
    Garzotti, L.
    et al.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics. CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    Scenario development for D-T operation at JET2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 7, article id 076037Article in journal (Refereed)
    Abstract [en]

    The JET exploitation plan foresees D-T operations in 2020 (DTE2). With respect to the first D-T campaign in 1997 (DTE1), when JET was equipped with a carbon wall, the experiments will be conducted in presence of a beryllium-tungsten ITER-like wall and will benefit from an extended and improved set of diagnostics and higher additional heating power (32 MW neutral beam injection + 8 MW ion cyclotron resonance heating). There are several challenges presented by operations with the new wall: a general deterioration of the pedestal confinement; the risk of heavy impurity accumulation in the core, which, if not controlled, can cause the radiative collapse of the discharge; the requirement to protect the divertor from excessive heat loads, which may damage it permanently. Therefore, an intense activity of scenario development has been undertaken at JET during the last three years to overcome these difficulties and prepare the plasmas needed to demonstrate stationary high fusion performance and clear alpha particle effects. The paper describes the status and main achievements of this scenario development activity, both from an operational and plasma physics point of view.

  • 10. Joffrin, E.
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Fridström, Richard
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Moon, Sunwoo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zychor, I
    et al.,
    Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112021Article in journal (Refereed)
    Abstract [en]

    For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.

  • 11. Khrapak, S. A.
    et al.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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 plasma2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 3, p. 35001-Article in journal (Refereed)
    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.

  • 12. Komm, M.
    et al.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cavalier, J.
    Dejarnac, R.
    Gunn, J. P.
    Podolnik, A.
    On thermionic emission from plasma-facing components in tokamak-relevant conditions2017In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 9, article id 094002Article in journal (Refereed)
    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.

  • 13. 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 experiments2017In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, article id 014069Article in journal (Refereed)
    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.

  • 14.
    Labit, B.
    et al.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Thorén, Emil
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vallejos Olivares, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    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 Upgrade2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 8, article id 086020Article in journal (Refereed)
    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.

  • 15.
    Lucco Castello, Federico
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Hansen, Jesper Schmidt
    Dyre, Jeppe C.
    Isomorph invariance and thermodynamics of repulsive dense bi-Yukawa one-component plasmas2019In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, no 5, article id 053705Article in journal (Refereed)
    Abstract [en]

    In numerous realizations of complex plasmas, dust-dust interactions are characterized by two screening lengths and are thus better described by a combination of Yukawa potentials. The present work investigates the static correlations and the thermodynamics of repulsive dense bi-Yukawa fluids based on the fact that such strongly coupled systems exhibit isomorph invariance. The strong virial-potential energy correlations are demonstrated with the aid of molecular dynamics simulations, an accurate analytical expression for the isomorph family of curves is obtained, and an empirical expression for the fluid-solid phase-coexistence line is proposed. The isomorph-based empirically modified hypernetted-chain approach, grounded on the ansatz of isomorph invariant bridge functions, is then extended to such systems and the resulting structural properties show an excellent agreement with the results of computer simulations. A simple and accurate closed-form expression is obtained for the excess internal energy of dense bi-Yukawa fluids by capitalizing on the compact parameterization offered by the Rosenfeld-Tarazona decomposition in combination with the Rosenfeld scaling, which opens up the energy route to thermodynamics.

  • 16. Meyer, H.
    et al.
    Eich, T.
    Beurskens, M.
    Coda, S.
    Hakola, A.
    Martin, P.
    Adamek, J.
    Agostini, M.
    Aguiam, D.
    Ahn, J.
    Aho-Mantila, L.
    Akers, R.
    Albanese, R.
    Aledda, R.
    Alessi, E.
    Allan, S.
    Alves, D.
    Ambrosino, R.
    Amicucci, L.
    Anand, H.
    Anastassiou, G.
    Andrebe, Y.
    Angioni, C.
    Apruzzese, G.
    Ariola, M.
    Arnichand, H.
    Arter, W.
    Baciero, A.
    Barnes, M.
    Barrera, L.
    Behn, R.
    Bencze, A.
    Bernardo, J.
    Bernert, M.
    Bettini, P.
    Bilkova, P.
    Bin, W.
    Birkenmeier, G.
    Bizarro, J. P. S.
    Blanchard, P.
    Blanken, T.
    Bluteau, M.
    Bobkov, V.
    Bogar, O.
    Boehm, P.
    Bolzonella, T.
    Boncagni, L.
    Botrugno, A.
    Bottereau, C.
    Bouquey, F.
    Bourdelle, C.
    Bremond, S.
    Brezinsek, S.
    Brida, D.
    Brochard, F.
    Buchanan, J.
    Bufferand, H.
    Buratti, P.
    Cahyna, P.
    Calabro, G.
    Camenen, Y.
    Caniello, R.
    Cannas, B.
    Canton, A.
    Cardinali, A.
    Carnevale, D.
    Carr, M.
    Carralero, D.
    Carvalho, P.
    Casali, L.
    Castaldo, C.
    Castejon, F.
    Castro, R.
    Causa, F.
    Cavazzana, R.
    Cavedon, M.
    Cecconello, M.
    Ceccuzzi, S.
    Cesario, R.
    Challis, C. D.
    Chapman, I. T.
    Chapman, S.
    Chernyshova, M.
    Choi, D.
    Cianfarani, C.
    Ciraolo, G.
    Citrin, J.
    Clairet, F.
    Classen, I.
    Coelho, R.
    Coenen, J. W.
    Colas, L.
    Conway, G.
    Corre, Y.
    Costea, S.
    Crisanti, F.
    Cruz, N.
    Cseh, G.
    Czarnecka, A.
    D'Arcangelo, O.
    De Angeli, M.
    De Masi, G.
    De Temmerman, G.
    De Tommasi, G.
    Decker, J.
    Delogu, R. S.
    Dendy, R.
    Denner, P.
    Di Troia, C.
    Dimitrova, M.
    D'Inca, R.
    Doric, V.
    Douai, D.
    Drenik, A.
    Dudson, B.
    Dunai, D.
    Dunne, M.
    Duval, B. P.
    Easy, L.
    Elmore, S.
    Erdos, B.
    Esposito, B.
    Fable, E.
    Faitsch, M.
    Fanni, A.
    Fedorczak, N.
    Felici, F.
    Ferreira, J.
    Fevrier, O.
    Ficker, O.
    Fietz, S.
    Figini, L.
    Figueiredo, A.
    Fil, A.
    Fishpool, G.
    Fitzgerald, M.
    Fontana, M.
    Ford, O.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fridstr, R.
    Frigione, D.
    Fuchert, G.
    Fuchs, C.
    Palumbo, M. Furno
    Futatani, S.
    Gabellieri, L.
    Galazka, K.
    Galdon-Quiroga, J.
    Galeani, S.
    Gallart, D.
    Gallo, A.
    Galperti, C.
    Gao, Y.
    Garavaglia, S.
    Garcia, J.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Garcia-Lopez, J.
    Garcia-Munoz, M.
    Gardarein, J. -L
    Garzotti, L.
    Gaspar, J.
    Gauthier, E.
    Geelen, P.
    Geiger, B.
    Ghendrih, P.
    Ghezzi, F.
    Giacomelli, L.
    Giannone, L.
    Giovannozzi, E.
    Giroud, C.
    Gleason Gonzalez, C.
    Gobbin, M.
    Goodman, T. P.
    Gorini, G.
    Gospodarczyk, M.
    Granucci, G.
    Gruber, M.
    Gude, A.
    Guimarais, L.
    Guirlet, R.
    Gunn, J.
    Hacek, P.
    Hacquin, S.
    Hall, S.
    Ham, C.
    Happel, T.
    Harrison, J.
    Harting, D.
    Hauer, V.
    Havlickova, E.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Helou, W.
    Henderson, S.
    Hennequin, P.
    Heyn, M.
    Hnat, B.
    Holzl, M.
    Hogeweij, D.
    Honore, C.
    Hopf, C.
    Horacek, J.
    Hornung, G.
    Horvath, L.
    Huang, Z.
    Huber, A.
    Igitkhanov, J.
    Igochine, V.
    Imrisek, M.
    Innocente, P.
    Ionita-Schrittwieser, C.
    Isliker, H.
    Ivanova-Stanik, I.
    Jacobsen, A. S.
    Jacquet, P.
    Jakubowski, M.
    Jardin, A.
    Jaulmes, F.
    Jenko, F.
    Jensen, T.
    Busk, O. Jeppe Miki
    Jessen, M.
    Joffrin, E.
    Jones, O.
    Jonsson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kallenbach, A.
    Kallinikos, N.
    Kalvin, S.
    Kappatou, A.
    Karhunen, J.
    Karpushov, A.
    Kasilov, S.
    Kasprowicz, G.
    Kendl, A.
    Kernbichler, W.
    Kim, D.
    Kirk, A.
    Kjer, S.
    Klimek, I.
    Kocsis, G.
    Kogut, D.
    Komm, M.
    Korsholm, S. B.
    Koslowski, H. R.
    Koubiti, M.
    Kovacic, J.
    Kovarik, K.
    Krawczyk, N.
    Krbec, J.
    Krieger, K.
    Krivska, A.
    Kube, R.
    Kudlacek, O.
    Kurki-Suonio, T.
    Labit, B.
    Laggner, F. M.
    Laguardia, L.
    Lahtinen, A.
    Lalousis, P.
    Lang, P.
    Lauber, P.
    Lazanyi, N.
    Lazaros, A.
    Le, H. B.
    Lebschy, A.
    Leddy, J.
    Lefevre, L.
    Lehnen, M.
    Leipold, F.
    Lessig, A.
    Leyland, M.
    Li, L.
    Liang, Y.
    Lipschultz, B.
    Liu, Y. Q.
    Loarer, T.
    Loarte, A.
    Loewenhoff, T.
    Lomanowski, B.
    Loschiavo, V. P.
    Lunt, T.
    Lupelli, I.
    Lux, H.
    Lyssoivan, A.
    Madsen, J.
    Maget, P.
    Maggi, C.
    Maggiora, R.
    Magnussen, M. L.
    Mailloux, J.
    Maljaars, B.
    Malygin, A.
    Mantica, P.
    Mantsinen, M.
    Maraschek, M.
    Marchand, B.
    Marconato, N.
    Marini, C.
    Marinucci, M.
    Markovic, T.
    Marocco, D.
    Marrelli, L.
    Martin, Y.
    Solis, J. R. Martin
    Martitsch, A.
    Mastrostefano, S.
    Mattei, M.
    Matthews, G.
    Mavridis, M.
    Mayoral, M. -L
    Mazon, D.
    McCarthy, P.
    McAdams, R.
    McArdle, G.
    McClements, K.
    McDermott, R.
    McMillan, B.
    Meisl, G.
    Merle, A.
    Meyer, O.
    Milanesio, D.
    Militello, F.
    Miron, I. G.
    Mitosinkova, K.
    Mlynar, J.
    Mlynek, A.
    Molina, D.
    Molina, P.
    Monakhov, I.
    Morales, J.
    Moreau, D.
    Morel, P.
    Moret, J. -M
    Moro, A.
    Moulton, D.
    Mueller, H. W.
    Nabais, F.
    Nardon, E.
    Naulin, V.
    Nemes-Czopf, A.
    Nespoli, F.
    Neu, R.
    Nielsen, A. H.
    Nielsen, S. K.
    Nikolaeva, V.
    Nimb, S.
    Nocente, M.
    Nouailletas, R.
    Nowak, S.
    Oberkofler, M.
    Oberparleiter, M.
    Ochoukov, R.
    Odstrcil, T.
    Olsen, J.
    Omotani, J.
    O'Mullane, M. G.
    Orain, F.
    Osterman, N.
    Paccagnella, R.
    Pamela, S.
    Pangione, L.
    Panjan, M.
    Papp, G.
    Paprok, R.
    Parail, V.
    Parra, I.
    Pau, A.
    Pautasso, G.
    Pehkonen, S. -P
    Pereira, A.
    Cippo, E. Perelli
    Ridolfini, V. Pericoli
    Peterka, M.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petrzilka, V.
    Piovesan, P.
    Piron, C.
    Pironti, A.
    Pisano, F.
    Pisokas, T.
    Pitts, R.
    Ploumistakis, I.
    Plyusnin, V.
    Pokol, G.
    Poljak, D.
    Poloskei, P.
    Popovic, Z.
    Por, G.
    Porte, L.
    Potzel, S.
    Predebon, I.
    Preynas, M.
    Primc, G.
    Pucella, G.
    Puiatti, M. E.
    Putterich, T.
    Rack, M.
    Ramogida, G.
    Rapson, C.
    Rasmussen, J. Juul
    Rasmussen, J.
    Ratta, G. A.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ravera, G.
    Refy, D.
    Reich, M.
    Reimerdes, H.
    Reimold, F.
    Reinke, M.
    Reiser, D.
    Resnik, M.
    Reux, C.
    Ripamonti, D.
    Rittich, D.
    Riva, G.
    Rodriguez-Ramos, M.
    Rohde, V.
    Rosato, J.
    Ryter, F.
    Saarelma, S.
    Sabot, R.
    Saint-Laurent, F.
    Salewski, M.
    Salmi, A.
    Samaddar, D.
    Sanchis-Sanchez, L.
    Santos, J.
    Sauter, O.
    Scannell, R.
    Scheffer, M.
    Schneider, M.
    Schneider, B.
    Schneider, P.
    Schneller, M.
    Schrittwieser, R.
    Schubert, M.
    Schweinzer, J.
    Seidl, J.
    Sertoli, M.
    Sesnic, S.
    Shabbir, A.
    Shalpegin, A.
    Shanahan, B.
    Sharapov, S.
    Sheikh, U.
    Sias, G.
    Sieglin, B.
    Silva, C.
    Silva, A.
    Fuglister, M. Silva
    Simpson, J.
    Snicker, A.
    Sommariva, C.
    Sozzi, C.
    Spagnolo, S.
    Spizzo, G.
    Spolaore, M.
    Stange, T.
    Pedersen, M. Stejner
    Stepanov, I.
    Stober, J.
    Strand, P.
    Susnjara, A.
    Suttrop, W.
    Szepesi, T.
    Tal, B.
    Tala, T.
    Tamain, P.
    Tardini, G.
    Tardocchi, M.
    Teplukhina, A.
    Terranova, D.
    Testa, D.
    Theiler, C.
    Thornton, A.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tophoj, L.
    Treutterer, W.
    Trevisan, G. L.
    Tripsky, M.
    Tsironis, C.
    Tsui, C.
    Tudisco, O.
    Uccello, A.
    Urban, J.
    Valisa, M.
    Vallejos, Pablo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Valovic, M.
    Van den Brand, H.
    Vanovac, B.
    Varoutis, S.
    Vartanian, S.
    Vega, J.
    Verdoolaege, G.
    Verhaegh, K.
    Vermare, L.
    Vianello, N.
    Vicente, J.
    Viezzer, E.
    Vignitchouk, L.
    Vijvers, W. A. J.
    Villone, F.
    Viola, B.
    Vlahos, L.
    Voitsekhovitch, I.
    Vondracek, P.
    Vu, N. M. T.
    Wagner, D.
    Walkden, N.
    Wang, N.
    Wauters, T.
    Weiland, M.
    Weinzettl, V.
    Westerhof, E.
    Wiesenberger, M.
    Willensdorfer, M.
    Wischmeier, M.
    Wodniak, I.
    Wolfrum, E.
    Yadykin, D.
    Zagorski, R.
    Zammuto, I.
    Zanca, P.
    Zaplotnik, R.
    Zestanakis, P.
    Zhang, W.
    Zoletnik, S.
    Zuin, M.
    Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 10, article id 102014Article in journal (Refereed)
    Abstract [en]

    Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement H-H(98,H-y2) approximate to 0.95. Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.

  • 17. Meyer, H.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Thorén, Emil
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Zohm, H.
    et al.,
    Overview of physics studies on ASDEX Upgrade2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112014Article in journal (Refereed)
    Abstract [en]

    The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q(95) = 5.5, beta(N) <= 2.8) at low density. Higher installed electron cyclotron resonance heating power <= 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with P-sep/R <= 11 MW m(-1) with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently H-H98(y,H-2) <= 1.1. This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of T-i and E-r allow for inter ELM transport analysis confirming that E-r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to n/n(GW) <= 0.7 have been characterised using beta-feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle-measured for the first time-or the cross-phase angle of T-e and n(e) fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow T-e profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvenic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.

  • 18.
    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, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. st Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy..
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    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 fluctuations2018In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 3, article id 905840308Article in journal (Refereed)
    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.

  • 19.
    Pucella, G.
    et al.
    ENEA, Fus & Nucl Safety Dept, CR Frascati, Via E Peuni 45, I-00044 Rome, Italy.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Zito, P.
    ENEA, Fus & Nucl Safety Dept, CR Frascati, Via E Peuni 45, I-00044 Rome, Italy.
    et al.,
    Overview of the FTU results2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112015Article in journal (Refereed)
    Abstract [en]

    Since the 2016 IAEA Fusion Energy Conference, FTU operations have been mainly devoted to experiments on runaway electrons and investigations into a tin liquid limiter; other experiments have involved studies of elongated plasmas and dust. The tearing mode onset in the high density regime has been studied by means of the linear resistive code MARS, and the highly collisional regimes have been investigated. New diagnostics, such as a runaway electron imaging spectroscopy system for in-flight runaway studies and a triple Cherenkov probe for the measurement of escaping electrons, have been successfully installed and tested, and new capabilities of the collective Thomson scattering and the laser induced breakdown spectroscopy diagnostics have been explored.

  • 20.
    Ratynskaia, S.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, P.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    De Angeli, M.
    CNR, Ist Fis Plasma, I-20125 Milan, Italy..
    Rohde, V.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Herrmann, A.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ripamonti, D.
    CNR, Inst Condensed Matter Chem & Energy Technol, I-20125 Milan, Italy..
    Riva, G.
    CNR, Inst Condensed Matter Chem & Energy Technol, I-20125 Milan, Italy..
    Thorén, E.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vignitchouk, L.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Sieglin, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Krieger, K.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Neu, R.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Interaction of metal dust adhered on castellated substrates with the ELMy H-mode plasmas of ASDEX-Upgrade2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 10, article id 106023Article in journal (Refereed)
    Abstract [en]

    Castellated substrates with adhered micron dust have been exposed in the outer ASDEX-Upgrade divertor to ELMy H-mode discharges. Beryllium proxy (chromium, copper) and refractory metal (tungsten, molybdenum) dust has been deposited on the plasma-facing and plasma-shadowed sides of the monoblocks as well as the bottom of the gaps. Interaction with time-averaged transient heat loads up to 5 MWm(-2) led to dust remobilization, clustering, melting and wetting-induced coagulation. The amount of dust released in the vessel has been quantified and remobilized dust trajectories inferred. Gaps can efficiently trap locally adhered dust, but dust detaching from adjacent monoblocks does not preferentially move inside the gaps implying that they do not constitute a dust accumulation site. Heat transfer simulations of melting events are also reported taking into account heat constriction due to the finite contact area and the presence of surface roughness.

  • 21.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dilecce, G.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    BABE - a brush cathode discharge for thermal fluctuation measurements2015In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, article id 345810202Article in journal (Refereed)
    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.

  • 22.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dilecce, G.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nitrogen optical emission during nanosecond laser ablation of metals: prompt electrons or photo-ionization?2014In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 117, no 1, p. 409-413Article in journal (Refereed)
    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.

  • 23.
    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.

  • 24.
    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.

  • 25.
    Ratynskaia, Svetlana V.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    De Angeli, M.
    CNR, Ist Fis Plasma, Via Cozzi 53, I-20125 Milan, Italy..
    Ripamonti, D.
    CNR, Inst Condensed Matter Chem & Energy Technol, Via Cozzi 53, I-20125 Milan, Italy..
    Riva, G.
    CNR, Inst Condensed Matter Chem & Energy Technol, Via Cozzi 53, I-20125 Milan, Italy..
    Aussems, D.
    DIFFER, De Zaale 20, NL-5612 AJ Eindhoven, Netherlands..
    Morgan, T. W.
    DIFFER, De Zaale 20, NL-5612 AJ Eindhoven, Netherlands..
    Interaction of adhered beryllium proxy dust with transient and stationary plasmas2018In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 17, p. 222-227Article in journal (Refereed)
    Abstract [en]

    Tungsten (W) substrates with adhered beryllium (Be) proxy dust-copper, chromium, aluminium -have been exposed in the Magnum-PSI linear device. Their interaction with transient and stationary plasmas has been systematically studied under varying heat fluxes and magnetic field topologies. The dust remobilization activities, macro-morphological changes and chemical modifications induced by the plasma incidence are documented. Aluminium is identified to be the most suitable surrogate material due to the similar binary phase diagram and nearly identical evaporation rates. Extrapolation suggests that Be dust cannot survive on hot W surfaces but it can trigger mixed Be/W effects prior to its plasma removal.

  • 26.
    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.

  • 27.
    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.

  • 28. Riva, G.
    et al.
    Tolias, Panagiotis
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Daminelli, G.
    Donde, R.
    De Angeli, M.
    Vassallo, E.
    Pedroni, M.
    Adhesion measurements for tungsten dust deposited on tungsten surfaces2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 593-598Article in journal (Refereed)
    Abstract [en]

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

  • 29. 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.

  • 30.
    Ström, Petter
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Simon
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    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.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Johnson, T.
    Stefanikova, E.
    Zhou, Y.
    Zychor, I.
    et al.,
    Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall2019In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 202-213Article in journal (Refereed)
    Abstract [en]

    Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analyzed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 micrometer were indicated, but typical values were on the order of a few hundred nanometers. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 micrometer were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

  • 31.
    Thorén, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bazylev, B.
    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. KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Krieger, K.
    Pitts, R. A.
    Pestchanyi, S.
    Komm, M.
    Sieglin, B.
    Simulations with current constraints of ELM-induced tungsten melt motion in ASDEX Upgrade2017In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, article id 014006Article in journal (Refereed)
    Abstract [en]

    Melt motion simulations of recent ASDEX Upgrade experiments on transient-induced melting of a tungsten leading edge during ELMing H-mode are performed with the incompressible fluid dynamics code MEMOS 3D. The total current flowing through the sample was measured in these experiments providing an important constraint for the simulations since thermionic emission is considered to be responsible for the replacement current driving melt motion. To allow for a reliable comparison, the description of the space-charge limited regime of thermionic emission has been updated in the code. The effect of non-periodic aspects of the spatio-temporal heat flux in the temperature distribution and melt characteristics as well as the importance of current limitation are investigated. The results are compared with measurements of the total current and melt profile.

  • 32.
    Thorén, Emil
    et al.
    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.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Pitts, R. A.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 St Paul Les Durance, France..
    Krieger, K.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Komm, M.
    Inst Plasma Phys CAS, Za Slovankou 3, Prague 18200 8, Czech Republic..
    Baken, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    MEMOS 3D modelling of ELM-induced transient melt damage on an inclined tungsten surface in the ASDEX Upgrade outer divertor2018In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 17, p. 194-199Article in journal (Refereed)
    Abstract [en]

    The first MEMOS 3D simulations of liquid metal motion on an inclined bulk tungsten sample transiently molten by edge-localized modes (ELMs) are reported. The exposures took place at the outer ASDEX-Upgrade divertor with the tungsten surface tangent intersecting the magnetic field at similar to 18 degrees. Simulations confirm that the observed poloidal melt motion is caused by the volumetric J x B force with J the bulk replacement current triggered by thermionic emission. The final erosion profile and total melt build up are reproduced by employing the escaping thermionic current dependence on the incident heat flux derived from dedicated particle-in-cell simulations. Modelling reveals that melt dynamics is governed by the volumetric Lorentz force, capillary flows due to thermal surface tension gradients and viscous deceleration. The effect of the evolving surface deformation, that locally alters the field-line inclination modifying the absorbed power flux and the escaping thermionic current, in the final surface morphology is demonstrated to be significant.

  • 33.
    Thorén, Emil
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    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.
    Pitts, R. A.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 St Paul Les Durance, France..
    Krieger, K.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Self-consistent description of the replacement current driving melt layer motion in fusion devices2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 10, article id 106003Article in journal (Refereed)
    Abstract [en]

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

  • 34.
    Tierens, W.
    et al.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Fridström, Richard
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Vallejos Olivares, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zuin, M.
    Consorzio RFX, Padua, Italy..
    et al.,
    Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 4, article id 046001Article in journal (Refereed)
    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.

  • 35.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Analytical expressions for thermophysical properties of solid and liquid tungsten relevant for fusion applications2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 13, p. 42-57Article in journal (Refereed)
    Abstract [en]

    The status of the literature is reviewed for several thermophysical properties of pure solid and liquid tungsten which constitute input for the modelling of intense plasma-surface interaction phenomena that are important for fusion applications. Reliable experimental data are analyzed for the latent heat of fusion, the electrical resistivity, the specific isobaric heat capacity, the thermal conductivity and the mass density from the room temperature up to the boiling point of tungsten as well as for the surface tension and the dynamic viscosity across the liquid state. Analytical expressions of high accuracy are recommended for these thermophysical properties that involved a minimum degree of extrapolations. In particular, extrapolations were only required for the surface tension and viscosity.

  • 36.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Lifshitz calculations of Hamaker constants for fusion relevant materials2018In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 133, p. 110-116Article in journal (Refereed)
    Abstract [en]

    The determination of the Hamaker constant is necessary for the quantification of the van der Waals force and thus of dust-wall adhesion. Here Lifshitz theory is employed for the calculation of the non-retarded Hamaker constants of ten common dust-wall material combinations. Extended-in-frequency reliable dielectric data are employed and two independent computational methods are considered for the calculation of the dielectric function at the imaginary Matsubara frequencies. The Hamaker constant for tungsten-on-tungsten is the largest calculated, which implies the strongest adhesion. The Hamaker constant for graphite-on-graphite is much smaller than tungsten-on-tungsten and even beryllium-on-beryllium. Copper, chromium and especially aluminium are identified to be proper adhesive proxies of beryllium.

  • 37.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Low-frequency electrostatic modes in partially ionized complex plasmas: a kinetic approach2012In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, p. 013002-Article in journal (Refereed)
    Abstract [en]

    A kinetic model of partially ionized complex plasmas is employed for the numerical analysis of low-frequency longitudinal modes for typical laboratory plasmas. The approach self-consistently includes the effects of plasma particle absorption on dust, collisions with neutrals and electron impact ionization. In addition to the typical dust acoustic mode, the results reveal the existence of a novel long-wavelength mode, attributed to the interplay between the mechanisms of plasma production and loss. The main properties of mode dispersions are investigated through their dependence on plasma and dust parameters.

  • 38.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    On electron backscattering from dust grains in fusion plasmas2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 4, p. 045003-Article in journal (Refereed)
    Abstract [en]

    Electron backscattering is identified as an important aspect of dust dynamics in fusion plasmas. Previously published experimental data on the backscattering of electrons with fusion relevant energies from solid targets are reviewed. Simple analytical expressions are proposed which, with a minimum number of parameters, can fit the experimental results with high accuracy. The contribution of electron backscattering to dust charging and heating is calculated. It is concluded that, especially for high-Z materials such as tungsten, electron backscattering leads to effective cooling of the grains, thus reducing the dust bulk temperature and enhancing dust lifetime and transport.

  • 39.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    On secondary electron emission and its semi-empirical description2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 12, p. 123002-Article, review/survey (Refereed)
    Abstract [en]

    The description of secondary electron emission, as presented by plasma-material interaction fusion compendia, is demonstrated to be outdated both in its theoretical and experimental aspects. As a consequence, the recommended treatment leads to a strong overestimation of the secondary electron emission yields for tokamak relevant materials. Reliable experimental data-sets, in fusion energy ranges, are identified after a detailed review of a recently updated electron-solid interaction database and previously published experimental results. A novel semi-empirical approach is proposed for the description of the secondary electron emission yield. Application of the approach for a large number of solids reveals an unprecedented agreement with experimental data. The present results can serve as a reliable input for future quantitative investigations of the effect of secondary electron emission on various aspects of scrape-off-layer physics.

  • 40.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The Klimontovich description of complex plasma systems: Low frequency electrostatic modes, spectral densities of fluctuations and collision integrals2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Plasmas seeded with solid particulates of nanometer to micron sizes (complex plasma systems) are a ubiquitous feature of intergalactic, interstellar and planetary environments but also of plasma processing applications or even fusion devices.

    Their novel aspects compared with ideal multi-component plasmas stem from (i) the large number of elementary charges residing on the grain surface, (ii) the variability of the charge over mass ratio of the dust component, (iii) the inherent openness and dissipative nature of such systems.

     

    Their statistical description presents a major challenge; On one hand by treating dust grains as point particles new phase space variables must be introduced augmenting the classical Hamiltonian phase space, while the microphysics of interaction between the plasma and the grains will introduce additional coupling between the kinetic equations of each species, apart from the usual fine-grained electromagnetic field coupling. On the other hand complex plasma systems do not always exist in a gaseous state but can also condensate, i.e. form liquid, solid or crystalline states.

     

    In this thesis we study gaseous partially ionized complex plasma systems from the perspective of the Klimontovich technique of second quantization in phase space. Initially, in regimes typical of dust dynamics. Starting from the Klimontovich equations for the exact phase space densities, theory deliverables such as the permittivity, the spectral densities of fluctuations and the collision integrals are implemented either for concrete predictions related to low frequency electrostatic waves or for diagnostic purposes related to the enhancement of the ion density and electrostatic potential fluctuation spectra due to the presence of dust grains. Particular emphasis is put to the comparison of the self-consistent kinetic model with multi-component kinetic models (treating dust as an additional massive charged species) as well as to the importance of the nature of the plasma particle source. Finally, a new kinetic model of complex plasmas (for both constant and fluctuating sources) is formulated. It is valid in regimes typical of ion dynamics, where plasma discreteness can no longer be neglected, and, in contrast to earlier models, does not require relatively large dust densities to be valid.

  • 41.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Castello, F. Lucco
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Isomorph-based empirically modified hypernetted-chain approach for strongly coupled Yukawa one-component plasmas2019In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, no 4, article id 043703Article in journal (Refereed)
    Abstract [en]

    Isomorph theory is employed in order to establish a mapping between the bridge function of Coulomb and Yukawa one-component plasmas. Within an exact invariance ansatz for the bridge functions and by capitalizing on the availability of simulation-extracted Coulomb bridge functions, an analytical Yukawa bridge function is derived which is inserted into the integral theory framework. In spite of its simplicity and computational speed, the proposed integral approach exhibits an excellent agreement with computer simulations of dense Yukawa liquids without invoking adjustable parameters. 

  • 42.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    De Angeli, M.
    CNR, Ist Fis Plasma, Via Corsi 53, I-20125 Milan, Italy..
    Riva, G.
    CNR, Inst Condensed Matter Chem & Energy Technol, Via Cozzi 53, I-20125 Milan, Italy..
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Daminelli, G.
    CNR, Inst Condensed Matter Chem & Energy Technol, Via Cozzi 53, I-20125 Milan, Italy..
    Laguardia, L.
    CNR, Ist Fis Plasma, Via Corsi 53, I-20125 Milan, Italy..
    Pedron, M.
    CNR, Ist Fis Plasma, Via Corsi 53, I-20125 Milan, Italy..
    Ripamonti, D.
    CNR, Inst Condensed Matter Chem & Energy Technol, Via Cozzi 53, I-20125 Milan, Italy..
    Uccello, A.
    CNR, Ist Fis Plasma, Via Corsi 53, I-20125 Milan, Italy..
    Vassallo, E.
    CNR, Ist Fis Plasma, Via Corsi 53, I-20125 Milan, Italy..
    The adhesion of tungsten dust on plasma-exposed tungsten surfaces2019In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 18, p. 18-22Article in journal (Refereed)
    Abstract [en]

    The adhesion of tungsten dust is measured on plasma-exposed and non-exposed tungsten substrates with the electrostatic detachment method. Tungsten substrates of comparable surface roughness have been exposed to the deuterium plasmas of the GyM linear device and the argon plasmas of rf glow discharges under conditions which invariably modify the surface composition due to physical sputtering. The adhesion has been systematically characterized for different spherical nearly monodisperse dust populations. Independent of the dust size, an approximate 50% post-exposure reduction of the average and spread of the adhesive force has been consistently observed and attributed to surface chemistry modifications.

  • 43.
    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.
    Scattering of radiation in collisionless dusty plasmas2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 4, p. 043706-Article in journal (Refereed)
    Abstract [en]

    Scattering of electromagnetic waves in collisionless dusty plasmas is studied in the framework of a multi-component kinetic model. The investigation focuses on the spectral distribution of the scattered radiation. Pronounced dust signatures are identified in the coherent spectrum due to scattering from the shielding cloud around the dust grains, dust acoustic waves, and dust-ion acoustic waves. The magnitude and shape of the scattered signal near these spectral regions are determined with the aid of analytical expressions and its dependence on the dust parameters is investigated. The use of radiation scattering as a potential diagnostic tool for dust detection is discussed.

  • 44.
    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.
    Screening in weakly ionized dusty plasmas; effect of dust density perturbations2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 2, p. 023702-Article in journal (Refereed)
    Abstract [en]

    The screening of the charge of a non-emitting dust grain immersed in a weakly ionized dusty plasma is studied on the basis of a self-consistent hydrodynamic description. The dust number density is considered large enough so that the test grain is not isolated from other grains and dust collective effects are important. Not only dust charge perturbations but also dust density perturbations are taken into account, the latter are shown to have a strong effect on both the short and long range part of the potential. The realization of collective attraction via the newly obtained potential is discussed, a mechanism that could be central to the understanding of phase-transitions and self-organization processes in dusty plasmas.

  • 45.
    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.

  • 46.
    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 Angelis, U.
    Kinetic models of partially ionized complex plasmas in the low frequency regime2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 7, p. 073705-Article in journal (Refereed)
    Abstract [en]

    The results from three kinetic models of complex plasmas taking into account collisions with neutrals are compared in the low-frequency regime: The "full" model which considers the absorption of plasma fluxes on dust particles and dust charge fluctuations, the "multi-component" model where both these effects are neglected, and the "standard" model which takes into account the dust charge perturbations but not the absorption of fluxes. We derive and numerically evaluate expressions of the low frequency responses of these models, also taking into account the modification of the capture cross-sections due to the effect of neutrals. The role of plasma sources and collisions with neutrals is assessed by computing the plasma permittivities and static permittivities for all the three models.

  • 47.
    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 Angelis, U.
    Regimes for experimental tests of kinetic effects in dust acoustic waves2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 10, p. 103707-Article in journal (Refereed)
    Abstract [en]

    The low frequency responses of a kinetic model of dusty plasma, taking into account the absorption of the plasma particles on the dust particles and fluctuations of dust charge, are evaluated numerically in order to identify realistic experimental parameter regimes where charging effects are dominant. A range of parameters in terms of dust number density and size as well as plasma densities, where significant differences with the multicomponent approach can be found, is proposed. General expressions for the imaginary parts of the low frequency responses are derived and numerical results for the damping rate in the corresponding ranges are provided to ensure that observations of dust-acoustic waves in those conditions are plausible.

  • 48.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Sezione di Napoli, Italy.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    de Angelis, U.
    Soft mean spherical approximation for dusty plasma liquids: Level of accuracy and analytic expressions2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 8, article id 083703Article in journal (Refereed)
    Abstract [en]

    The soft mean spherical approximation is employed for the study of the thermodynamics of dusty plasma liquids, the latter treated as Yukawa one-component plasmas. Within this integral theory method, the only input necessary for the calculation of the reduced excess energy stems from the solution of a single non-linear algebraic equation. Consequently, thermodynamic quantities can be routinely computed without the need to determine the pair correlation function or the structure factor. The level of accuracy of the approach is quantified after an extensive comparison with numerical simulation results. The approach is solved over a million times with input spanning the whole parameter space and reliable analytic expressions are obtained for the basic thermodynamic quantities.

  • 49.
    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 Angelis, U.
    Soft mean spherical approximation for dusty plasma liquids: One- component Yukawa systems with plasma shielding2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 90, no 5, p. 053101-Article in journal (Refereed)
    Abstract [en]

    The structure and thermodynamics of strongly coupled dusty plasmas are investigated with the soft mean spherical approximation. This integral theory approach is analytically solvable for Yukawa pair interactions yielding a closed-form solution for the direct correlation function. The pair correlation function, the structure factor, and basic thermodynamic quantities are calculated for a wide range of parameters. Exact consistency between the "energy"-"virial" thermodynamic routes and approximate consistency between the "energy" "compressibility" paths is demonstrated. Comparison with extensive molecular dynamics results is carried out and a remarkable agreement from the Coulomb limit to the strongly screened limit is revealed. The soft mean spherical approximation is concluded to be particularly well suited for the study of dusty plasma liquids, uniquely combining simplicity and accuracy.

  • 50.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Istituto Nazionale di Fisica Nucleare (INFN), Italy.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angelis, U.
    Lazzaro, E.
    The finite probe size effect in fluctuation measurements; application to dusty plasmas2016In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 82, no 2, article id 615820201Article in journal (Refereed)
    Abstract [en]

    The effect of the finite probe size in plasma fluctuation measurements is revisited for dusty plasmas, where it has been argued that dust leads to a significant low-frequency enhancement in the spectral densities of ion density fluctuations, which can constitute the physical basis of a dust diagnostic technique. Theoretical predictions for the spectral modifications are presented and the dust acoustic mode contribution is analysed. The finite probe size effect is treated within the volume average approach, which introduces geometry dependent form factors that are calculated for spherical and cylindrical probes. The volume average approach is compared with the typically employed cutoff wavenumber approximation for various dust and plasma parameters. The contribution of temperature fluctuations to the spectral density of current fluctuations is also evaluated.

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