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  • 301.
    Höök, Josef
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    An Adaptive delta f Monte Carlo Method2010In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, no 9, p. 2190-2197Article in journal (Refereed)
    Abstract [en]

    A new adaptive delta f Monte Carlo method is presented with an application to radio frequency heating and transport in fusion plasmas. The method is suitable when an initial zeroth-order approximation of the distribution function is known. The difference between our method and earlier delta f methods is that we model the source term, obtained from the delta f ansatz, by adding particles. The rate of particles is defined by the inhomogeneous term in the Fokker-Planck equation. We develop an adaptive scheme for modifying the unperturbed part G(x) such that the number of particles used in the simulation for a fixed weight is minimized. This implicitly reduces the variance and improves computational efficiency. The method is tested on a one-dimensional Fokker-Planck model for RF-heating and compared against the analytical stationary solution.

  • 302.
    Höök, L. Josef
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Composition schemes for the stochastic differential equation describing collisional pitch-angle diffusion2014In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 185, no 2, p. 590-594Article in journal (Refereed)
    Abstract [en]

    Two new second order accurate Monte Carlo integration schemes are derived for the stochastic differential equation describing pitch-angle scattering by Coulomb collisions in magnetized plasmas. Here the pitch-angle is the angle between the magnetic field and the particle velocity vectors. Mathematically this collision process corresponds to diffusion in the polar angle of a spherical coordinate system. The schemes are simple to implement, they are naturally bounded to the solution domain and their convergences are shown to compare favourably against commonly used alternative integration schemes.

  • 303.
    Höök, Lars Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kernel density estimation using the RBF-Galerkin method2012Report (Other academic)
  • 304.
    Höök, Lars Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Numerical solution of quasilinear kinetic diffusion equations in toroidal plasmas2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    One of the main challenges for the realization of a working fusion power plant is an increased detailed understanding of kinetic phenomena in toroidal plasmas. The tokamak is a toroidal, magnetically confined plasma device and is currently the main line towards a power plant. The spatial and temporal scales in a tokamak plasma are extreme and the only tractable path for quantitative studies is to rely on computer simulations. Present day simulation codes can resolve only some of these scales. Nevertheless they still require the largest high performance computing (HPC) resources available in the world. In combination with the increase of computational performance, it is therefore necessary to improve the numerical algorithms used in the simulations.

    In this thesis we have developed new numerical methods designed for Monte Carlo simulation of plasma kinetic diffusion. Examples are simulation of fast-ion thermalization and radio-frequency heating. The aim has been to reduce the statistical random noise in particle codes, produced by a finite number of particles (or markers). Traditionally the statistical noise is improved by increasing the number of particles (N) or by simulating the perturbation of the distribution (with particles) from a known distribution function. This is the well known δf method. In this thesis we have developed a new type of δf method, which minimizes the number of particles used in a simulation. The computational speedup of the new method is substantial. In this thesis, we have further benchmarked quasi-Monte Carlo techniques that improve the convergence rate from N−1/2 to N−1 for some cases.

    In Monte Carlo simulations, error appears also from the time step discretization. Based on the mathematics of operator splitting, a new scheme for the pitch-angle scattering diffusion process has been developed that outperforms the standard methods. Finally this thesis also presents a new code, SELFO-light, for self-consistent simulations of ion cyclotron resonance heating, suitable for routine calculations, which couples a one dimensional Fokker-Planck model with the finite element wave solver LION.

  • 305.
    Höök, Lars Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Variance reduction methods for numerical solution of plasma kinetic diffusion2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Performing detailed simulations of plasma kinetic diffusion is a challenging task and currently requires the largest computational facilities in the world. The reason for this is that, the physics in a confined heated plasma occur on a broad range of temporal and spatial scales. It is therefore of interest to improve the computational algorithms together with the development of more powerful computational resources. Kinetic diffusion processes in plasmas are commonly simulated with the Monte Carlo method, where a discrete set of particles are sampled from a distribution function and advanced in a Lagrangian frame according to a set of stochastic differential equations. The Monte Carlo method introduces computational error in the form of statistical random noise produced by a finite number of particles (or markers) N and the error scales as αNβ where β = 1/2 for the standard Monte Carlo method. This requires a large number of simulated particles in order to obtain a sufficiently low numerical noise level. Therefore it is essential to use techniques that reduce the numerical noise. Such methods are commonly called variance reduction methods. In this thesis, we have developed new variance reduction methods with application to plasma kinetic diffusion. The methods are suitable for simulation of RF-heating and transport, but are not limited to these types of problems. We have derived a novel variance reduction method that minimizes the number of required particles from an optimization model. This implicitly reduces the variance when calculating the expected value of the distribution, since for a fixed error the  optimization model ensures that a minimal number of particles are needed. Techniques that reduce the noise by improving the order of convergence, have also been considered. Two different methods have been tested on a neutral beam injection scenario. The methods are the scrambled Brownian bridge method and a method here called the sorting and mixing method of L´ecot and Khettabi[1999]. Both methods converge faster than the standard Monte Carlo method for modest number of time steps, but fail to converge correctly for large number of time steps, a range required for detailed plasma kinetic simulations. Different techniques are discussed that have the potential of improving the convergence to this range of time steps.

  • 306.
    Höök, Lars Josef
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Multilevel Monte Carlo and control-variate simulation of Coulomb collisionsManuscript (preprint) (Other academic)
  • 307.
    Höök, Lars Josef
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Randomized quasi-Monte Carlo simulation of fast-ion thermalization2012In: Computational Science & Discovery, ISSN 1749-4680, E-ISSN 1749-4699, Vol. 5, no 1, p. 014010-Article in journal (Refereed)
    Abstract [en]

    This work investigates the applicability of the randomized quasi-Monte Carlo method for simulation of fast-ion thermalization processes in fusion plasmas, e.g. for simulation of neutral beam injection and radio frequency heating. In contrast to the standard Monte Carlo method, the quasi-Monte Carlo method uses deterministic numbers instead of pseudo-random numbers and has a statistical weak convergence close to O(N -1), where N is the number of markers. We have compared different quasi-Monte Carlo methods for a neutral beam injection scenario, which is solved by many realizations of the associated stochastic differential equation, discretized with the Euler-Maruyama scheme. The statistical convergence of the methods is measured for time steps up to 2 14.

  • 308.
    Höök, Lars Josef
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Äkäslompolo, S.
    Composition schemes forthe stochastic differential equation describing collisional pitch-angle diffusionArticle in journal (Other academic)
  • 309. Ingesson, L. C.
    et al.
    Campbell, D. J.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ciattaglia, E.
    Dirken, P.
    Hawkes, N.
    Walsh, M.
    von Hellermann, M.
    Kalvin, S.
    McCarthy, P.
    Neubauer, O.
    Petrizzi, L.
    Progress on common aspects of the EU-supplied ITER diagnostics and prediction of diagnostic performance2006In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, no 10, p. 10F502-Article in journal (Refereed)
    Abstract [en]

    The European Union will supply a number of diagnostics for ITER. Significant progress has been made on the design and integration of these diagnostics. Specific topics, in common for several of the diagnostics, discussed are port-plug integration, simplification of labyrinths against neutron streaming, and design measures to protect and to be able to replace sensitive optical components. Performance analysis to predict the likely capability of the diagnostics to meet the ITER measurement requirements will be an important aspect of the design process. The interpretation of the measurement requirements, specifically of spatial resolution in the case of indirect measurements, is discussed on the basis of two examples, and methods of performance analysis are compared.

  • 310.
    Ivanova, Darya
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fuel retention and fuel removal from first wall components in tokamaks2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for a steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in the on-going Ph.D. work in order to contribute to the better understanding and development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom).

     This thesis provides an account on studies of fuel removal techniques from plasmafacing components (PFCs) and on consequences of dust formation. Following issues are addressed: (a)  properties of carbon and metal dust formed in the TEXTOR tokamak;  (b)  dust generation associated with removal of fuel and co-deposited layers from carbon PFCs from TEXTOR and Tore Supra;  (c)  surface morphology of wall components after different cleaning treatments;  (d)  surface properties of diagnostic mirrors tested at JET for ITER. The study dealt with carbon, tungsten and beryllium, i.e. with the three major elements being used for PFC in present-day devices and foreseen for a next-step machine.

     Some essential results are summarised by the following.

     (i)  The amount of loose dust found on the floor of the TEXTOR liner does not exceed 2 grams with particle size range 0.1 mm – 1 mm. The presence of fine (up to 1 mm) crystalline graphite in the collected matter suggests that brittle destruction of carbon PFC could take place during off-normal events. Carbon is the main component, but there are also magnetic and non-magnetic metal agglomerates. The results obtained strongly indicate that in a carbon wall machine the disintegration of flaking co-deposits on PFC is the main source of dust:  (ii)  The fuel content in dust and co-deposits varies from 10% on the main limiters to 0.03% on the neutralizer plates as determined by thermal desorption and ionbeam methods:  (iii)  Fuel removal by annealing in vacuum or by oxidative methods disintegrates codeposits. In the case of thick layers, the treatment makes them brittle thus reducing the adherence to the target and, as a consequence, this leads to the formation of dust:  (iv)   Application of thermal methods for fuel removal from carbon-rich layers is effective only at high temperatures (above 800 K), i.e. in the range exceeding the allowed baking temperature of the ITER divertor:  (v)   Photonic cleaning by laser pulses effectively removes fuel-rich deposited layers, but it also produces debris, especially under ablation conditions:  (vi)  Photonic cleaning of mirrors exposed in JET results in partial recovery of reflectivity, but surfaces are modified by laser pulses.

    The presentation of results is accompanied by a discussion of their consequences for the future development and the application of fuel and dust removal methods in a next-step fusion device.

  • 311.
    Ivanova, Darya
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Plasma-Facing Components in Tokamaks: Material Modification and Fuel Retention2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for the steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in this thesis in order to contribute to a better understanding and the development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in the Nuclear Research Center Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). Following issues were addressed: (a) properties of material migration products, i.e. co-deposited layers and dust particles; (b) impact of fuel removal methods on dust generation and on modification of plasma-facing components; (c) efficiency of fuel and deposit removal techniques; (d) degradation mechanism of diagnostic components - mirrors - and methods of their regeneration.

  • 312.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Likonen, Jari
    Widdowson, Anna
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    De Temmerman, Gregory
    Assessment of Cleaning Methods for First Mirrors Tested in JET for ITER2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S1241-S1244Article in journal (Refereed)
    Abstract [en]

    Two cleaning techniques were used for removal of co-deposits from the tested first mirrors exposed in JET: (a) ultrasonic bath; (b) a broad range of polishing conditions from manual buffing to machine polishing with the diamond grain size of up to 3 lm. Reflectivity measurements were performed after each step in the cleaning procedure. Surfaces were also examined with electron microscopy and ion beam analysis methods. Ultrasonic cleaning leads to partial recovery of reflectivity due to enhanced detachment of deposits. Typically 30-50% of the original reflectivity was recovered in the visible light and 50-90% in the infrared region. One mirror was cleaned completely. Polishing with diamond paste may lead to successful removal of deposits but the damage to the surface in case of the large diamond grains was observed. Recovery of up to 100% of the initial reflectivity was achieved for some mirrors.

  • 313.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Philipps, V.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Freisinger, M.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Huang, Z.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Penkalla, H.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Schweer, B.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Sergienko, G.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Sundelin, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Wessel, E.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Survey of dust formed in the TEXTOR tokamak: structure and fuel retention2009In: Physica scripta. T, ISSN 0281-1847, Vol. T138, p. 014025-Article in journal (Refereed)
    Abstract [en]

    A detailed survey of erosion and deposition on plasma-facing components was performed in the TEXTOR tokamak. Co-deposits and dust particles were collected from graphite limiters and from several locations on the Inconel liner. The total amount of dust (loose material), originating mainly from carbon-rich co-deposits detached from the limiters and the liner, was around 2 g, with sizes from 0.1 mu m to 1 mm. The morphology and fuel retention was determined using microscopy methods, ion beam analysis and thermal desorption spectrometry. The study revealed differences in structure and fuel content between deposits from the toroidal and main poloidal limiters. There were also splashes, up to 1 mm in diameter, of molten metal (mainly nickel) on the toroidal limiters. Issues of the dust conversion factor (erosion-to-dust) are addressed and a comparison with results of previous dust surveys at TEXTOR is also briefly presented.

  • 314.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Philipps, V.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Schweer, B.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Freisinger, M.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Huber, A.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Gierse, N.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Penkalla, H.
    Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
    Petersson, P.
    Ångström Laboratory, Uppsala University, Association EURATOM-VR.
    Dittmar, T.
    CEA-Cadarche, IRFM, Association EURATOM-CEA, France.
    Laser-based and thermal methods for fuel removal and cleaning of plasma-facing components2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S801-S804Article in journal (Refereed)
    Abstract [en]

    The efficiency of two methods for in-situ fuel removal has been tested on carbon and tungsten limiters retrieved from the TEXTOR and Tore Supra tokamaks: laser-inducedablation of co-deposits and annealing in vacuum at elevated temperature. The analyses of gas phase and surfaces performed with thermal desorption spectrometry, optical spectroscopy, ion beam analysis, surface profilometry and microscopy methods have shown: (i) the ablation leads to the generation of dust particles of 50 nm – 2μm; (ii) volatile products of ablation undergo condensation on surrounding surfaces; (iii) D/C ratio in such condensate is in the range 0.02-0.03; (iv) long-term annealing of 623 K for 70 hours results in release of not more ~10 % of deuterium accumulated in plasma-facing components; (v) effective removal is reached by heating to 900-1300 K.

  • 315.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kreter, A.
    Möller, S.
    Philipps, V.
    Freisinger, M.
    Wauters, T.
    Impact of thermal treatment and ICWC on fuel inventory in Co-deposits2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: volume 1, 2012, p. 317-320Conference paper (Refereed)
  • 316.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Philipps, V.
    Institute of Energy Research, Forschungszentrum Jülich.
    Freisinger, M.
    Institute of Energy Research, Forschungszentrum Jülich.
    Dittmar, T.
    CEA-Cadarache, IRFM.
    Huber, A.
    Institute of Energy Research, Forschungszentrum Jülich.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Schweer, B.
    Institute of Energy Research, Forschungszentrum Jülich.
    Sergienko, G.
    Institute of Energy Research, Forschungszentrum Jülich.
    Wessel, E.
    Institute of Energy Research, Forschungszentrum Jülich.
    Dust Particles in Controlled Fusion Devices: Generation Mechanism and Analysis2010Conference paper (Refereed)
    Abstract [en]

    Generation and in-vessel accumulation of carbon and metal dust are perceived to be serious safety andeconomy issues for a steady-state operation of a fusion reactor, e.g. ITER. This contribution provides acomprehensive account on: (a) properties of carbon and metal dust formed in the TEXTOR tokamak; (b) dustgeneration associated with removal of fuel and co-deposit from carbon PFC from TEXTOR and Tore Supra; (c)surface morphology of wall components after different cleaning treatments. The amount of loose dust found on thefloor of the TEXTOR liner does not exceed 2 grams with particle size range 0.1 m – 1 mm. The presence of fine(up to 1 m) crystalline graphite in the collected matter suggests that brittle destruction of carbon PFC could takeplace during off-normal events. Carbon is the main component, but there are also magnetic and non-magnetic metalagglomerates. The fuel content in dust and co-deposits varies from 10% on the main limiters to 0.03% on theneutralizer plates. Fuel removal by oxidative methods or by annealing in vacuum disintegrates co-deposits and, in thecase of thick layers, makes them brittle thus reducing the adherence to the target. Also photonic cleaning by laserpulses produces debris, especially under ablation conditions. The results obtained strongly indicate that in a carbonwall machine the disintegration of flaking co-deposits on PFC is the main source of dust.

  • 317.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Philipps, Volker
    Institute for Energy and Climate Research, Plasma Physics, Forschungszentrum Jülich.
    Schweer, Bernd
    Institute for Energy and Climate Research, Plasma Physics, Forschungszentrum Jülich.
    Petersson, Per
    Ångström Laboratory, Uppsala University.
    Freisinger, Michaele
    Institute for Energy and Climate Research, Plasma Physics, Forschungszentrum Jülich.
    Schmidt, Axel
    Institute for Energy and Climate Research, Plasma Physics, Forschungszentrum Jülich.
    Fuel re-absorption by thermally treated co-deposited carbon layers2011In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, p. 014006-Article in journal (Refereed)
    Abstract [en]

    Systematic studies have been conducted to address the fuel re-absorption by carbon deposits under repeated exposure to plasma after cleaning procedures. The investigation was done with graphite tiles from ALT-II (Advanced Limiter Test II), i.e. the main limiter at the TEXTOR tokamak. Pure graphite plates were used as the reference material. The experimental programme comprised the following: pre-characterization of specimens; D desorption by baking the tile at 1273 K; surface analyses of the fuel-depleted layers; exposure to deuterium in a laboratory plasma device and in TEXTOR; and quantitative assessment of deuterium re-absorption. The main result is that fuel retention in the re-exposed deposits is 30–40 times lower than that in the original co-deposit, showing that fuel re-absorption does not lead to an immediate re-saturation of deposits. Annealing at high temperatures enhances layer brittleness, leading eventually to detachment of co-deposits.

  • 318.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Widdowson, A.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Likonen, J.
    Marot, L.
    Alves, E.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Pintsuk, G.
    An overview of the comprehensive First Mirror Test in JET with ITER-like wall2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, p. 014011-Article in journal (Refereed)
    Abstract [en]

    The First Mirror Test in Joint European Torus (JET) with the International Thermonuclear Experimental Reactor-like wall was performed with polycrystalline molybdenum mirrors. Two major types of experiments were done. Using a reciprocating probe system in the main chamber, a short-term exposure was made during a 0.3 h plasma operation in 71 discharges. The impact on reflectivity was negligible. In a long-term experiment lasting 19 h with 13 h of X-point plasma, 20 Mo mirrors were exposed, including four coated with a 1 mu m-thick Rh layer. Optical performance of all mirrors exposed in the divertor was degraded by up to 80% because of beryllium, carbon and tungsten co-deposits on surfaces. Total reflectivity of most Mo mirrors facing plasma in the main chamber was only slightly affected in the spectral range 400-1600 nm, while the Rh-coated mirror lost its high original reflectivity by 30%, thus decreasing to the level typical of molybdenum surfaces. Specular reflectivity was decreased most strongly in the 250-400 nm UV range. Surface measurements with x-ray photoelectron spectroscopy and depth profiling with secondary ion mass spectrometry and heavy-ion elastic recoil detection analysis (ERDA) revealed that the very surface region on both types of mirrors had been modified by neutrals, resulting eventually in the composition change: Be, C, D at the level below 1x10(16) cm(-2) mixed with traces of Ni, Fe in the layer 10-30 nm thick. On several exposed mirrors, the original matrix material (Mo) remained as the major constituent of the modified layer. The data obtained in two major phases of the JET operation with carbon and full metal walls are compared. The implications of these results for first mirrors and their maintenance in a reactor-class device are discussed.

  • 319.
    Ivanova, Darya
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Widdowson, A.
    CCFE/EURATOM Fusion Association, Culham Science Centre.
    Likonen, J.
    Association EURATOM–TEKES, VTT, Espoo.
    Marot, L.
    Department of Physics, University of Basel.
    Koivuranta, K.
    EURATOM-TEKES, VTT.
    Coad, J. P.
    CCFE/EURATOM Fusion Association, Culham Science Centre.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Temmerman, G. De
    FOM Institute for Plasma Physics.
    Petersson, P.
    Ångström Laboratory, Uppsala University.
    Assessment of cleaning methods for rst mirrors tested in JET for ITERArticle in journal (Other academic)
  • 320. Jacob, Wolfgang
    et al.
    Linsmeier, Christian
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    13th International Workshop on Plasma-Facing Materials and Components for Fusion Applications/1st International Conference on Fusion Energy Materials Science2011In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, p. 011001-Article in journal (Other academic)
  • 321. Joffrin, E.
    et al.
    Baruzzo, M.
    Beurskens, M.
    Bourdelle, C.
    Brezinsek, S.
    Bucalossi, J.
    Buratti, P.
    Calabro, G.
    Challis, C. D.
    Clever, M.
    Coenen, J.
    Delabie, E.
    Dux, R.
    Lomas, P.
    de la Luna, E.
    de Vries, P.
    Flanagan, J.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frigione, D.
    Giroud, C.
    Groth, M.
    Hawkes, N.
    Hobirk, J.
    Lehnen, M.
    Maddison, G.
    Mailloux, J.
    Maggi, C. F.
    Matthews, G.
    Mayoral, M.
    Meigs, A.
    Neu, R.
    Nunes, I.
    Puetterich, T.
    Rimini, F.
    Sertoli, M.
    Sieglin, B.
    Sips, A. C. C.
    van Rooij, G.
    Voitsekhovitch, I.
    First scenario development with the JET new ITER-like wall2014In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, no 1, p. 013011-Article in journal (Refereed)
    Abstract [en]

    In the recent JET experimental campaigns with the new ITER-like wall (JET-ILW), major progress has been achieved in the characterization and operation of the H-mode regime in metallic environments: (i) plasma breakdown has been achieved at the first attempt and X-point L-mode operation recovered in a few days of operation; (ii) stationary and stable type-I ELMy H-modes with beta(N) similar to 1.4 have been achieved in low and high triangularity ITER-like shape plasmas and are showing that their operational domain at H = 1 is significantly reduced with the JET-ILW mainly because of the need to inject a large amount of gas (above 10(22) Ds(-1)) to control core radiation; (iii) in contrast, the hybrid H-mode scenario has reached an H factor of 1.2-1.3 at beta(N) of 3 for 2-3 s; and, (iv) in comparison to carbon equivalent discharges, total radiation is similar but the edge radiation is lower and Z(eff) of the order of 1.3-1.4. Strong core radiation peaking is observed in H-mode discharges at a low gas fuelling rate (i. e. below 0.5 x 10(22) Ds(-1)) and low ELM frequency (typically less than 10 Hz), even when the tungsten influx from the diverter is constant. High-Z impurity transport from the plasma edge to the core appears to be the dominant factor to explain these observations. This paper reviews the major physics and operational achievements and challenges that an ITER-like wall configuration has to face to produce stable plasma scenarios with maximized performance.

  • 322. Joffrin, E
    et al.
    De Vries, P
    Baruzzo, M
    Beurskens, M
    Bourdelle, C
    Bucalossi, J
    Brezinsek, S
    Calabro, C
    Challis, C
    Clever, M
    Coenen, J
    Delabie, E
    Dux, R
    Lomas, P
    de la Luna, E
    Flanagan, J
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frigione, D
    Giroud, C
    Groth, M
    Hawks, N
    Hobirk, J
    Lehnen, J
    Maddison, G
    Mailleaux, M
    Maggi, C
    Matthews, G
    Mayoral, M
    Meigs, M
    Neu, R
    Nunes, I
    Scenarios Development at JET with the New ITER-like Wall2012In: 24th IAEA Fusion Energy Conference - IAEA CN-197: Book of abstracts, 2012, p. EX/1-1-Conference paper (Refereed)
  • 323. Joffrin, E.
    et al.
    Tamain, P.
    Belonohy, E.
    Bufferand, H.
    Buratti, P.
    Challis, C. D.
    Delabie, E.
    Drewelow, P.
    Dodt, D.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Garcia, J.
    Giroud, C.
    Groth, M.
    Hobirk, J.
    Jarvinen, A. E.
    Kim, H. -T
    Koechl, F.
    Kruezi, U.
    Lipschutz, B.
    Lomas, P. J.
    de la Luna, E.
    Loarer, T.
    Maget, P.
    Maggi, C.
    Matthews, G.
    Maviglia, F.
    Meigs, A.
    Nunes, I.
    Pucella, G.
    Rimini, F.
    Saarelma, S.
    Solano, E.
    Sips, A. C. C.
    Tsalas, M.
    Voitsekhovitch, I.
    Weisen, H.
    Impact of divertor geometry on H-mode confinement in the JET metallic wall2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 8, article id 086025Article in journal (Refereed)
    Abstract [en]

    Recent experiments with the ITER-like wall have demonstrated that changes in divertor strike point position are correlated with strong modification of the global energy confinement. The impact on energy confinement is observable both on the pedestal confinement and core normalised gradients. The corner configuration shows an increased core density gradient length and ion pressure indicating a better ion confinement. The study of neutral re-circulation indicates the neutral pressure in the main chamber varies inversely with the energy confinement and a correlation between the pedestal total pressure and the neutral pressure in the main chamber can be established. It does not appear that charge exchange losses nor momentum losses could explain this effect, but it may be that changes in edge electric potential are playing a role at the plasma edge. This study emphasizes the importance of the scrape-off layer (SOL) conditions on the pedestal and core confinement.

  • 324.
    Johansson, Lars
    et al.
    Kalmar University.
    Rubel, Marek J.KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    17th International Vacuum Congress (IVC-17), 13th International Conference on Surface Science (ICSS-13) and International Conference on Nanoscience and technology (ICN+T 2007)2008Conference proceedings (editor) (Refereed)
  • 325.
    Johnson, T.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lönnroth, J.
    de Vries, P. C.
    Salmi, A.
    Eriksson, L.-G.
    Hynönen, V.
    Jenkins, I.
    Ongena, J.
    Oyama, N.
    Parail, V.
    Saibene, G.
    Sharapov, S.
    Shinohara, K.
    Modelling of Fast Particle Transport and Losses with TF Ripple in JET2007Conference paper (Other academic)
    Abstract [en]

    In preparation for ripple experiments at JET the heat loads from fast ions to plasma facing components were calculated by orbit following Monte Carlo codes. The calculations show that losses are generated by two mechanisms, ripple-trapping and ripple-banana diffusion, and that the heat loads could cause damage to plasma facing components. During the experiments the auxiliary power was therefore kept below the limits inferred from the simulations. Measurements of the losses of fast ions from NBI using visible-light and infrared cameras have been shown to be in agreement with the predictions from the simulations. Finally, interactions between fast ions and the non-axisymmetric magnetic field are shown to generate a toroidal torque, which in JET with ~1% ripple is of the same order as that from neutral beam injection.

  • 326. Johnson, Thomas
    et al.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, Lars-Göran
    Analysis of a quasilinear model for ion-cyclotron interactions in tokamaks2005In: Radio Frequency Power in Plasmas / [ed] Wukitch, SJ; Bonoli, PT, MELVILLE: AMER INST PHYSICS , 2005, Vol. 787, p. 54-57Conference paper (Refereed)
    Abstract [en]

    The quasilinear diffusion coefficient deviates significantly from the lowest order Larmor radius scaling D proportional to nu(2n)(perpendicular to). This is not only caused by the finite Larmor radius effects, but also by the inhomogeneous electric field polarisation and the changes of the guiding centre orbits. The regions with strong interaction and the boundaries for resonant interaction are identified. At these boundaries the quasi linear diffusion coefficient becomes discontinuous. Anew Monte Carlo scheme has been developed to treat problems with discontinuous diffusion coefficients.

  • 327.
    Johnson, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hynönen, V.
    Parail, V.
    Jenkins, I.
    Kiviniemi, T.
    Kurki-Suonio, T.
    Lönnroth, J.
    Salmi, A.
    Numerical Modelling of Ripple Induced Transport2006In: Proceedings of the 33rd EPS Conference on Plasma Physics, 2006, p. 408-411Conference paper (Other academic)
    Abstract [en]

    The ASCOT code has been used to analyse transport and calculate the thermal conductivity in plasmas with toroidal field ripple. The scaling of the thermal conductivity with dimensionless plasma parameters is similar to transport in the ripple plateau regime [1]. The ripple in machines with toroidal field coils similar to those in JET and JT-60U are quite different; while the maximum ripple is larger with 16 JET coils, the ripple at the X-point is larger with the JT-60U coils. The results are that the heat conductivity is similar in the two plasmas, while the particle losses are higher with the JT-60U coils.

  • 328.
    Johnson, Thomas J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn A. K.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, L. G.
    Analysis of a quasilinear model for ion cyclotron interactions in tokamaks2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 7, p. S433-S441Article in journal (Refereed)
    Abstract [en]

    An orbit averaged quasilinear operator for resonant ion cyclotron interactions is analysed. The regions in phase space where the interactions are strong and the boundaries between regions with resonant and non-resonant ion orbits are identified. At these boundaries the quasilinear diffusion coefficient becomes discontinuous, causing the standard Monte Carlo scheme to induce an unphysical flow of test particles into the region with lower diffusion coefficient. A new Monte Carlo scheme that balances the flows across discontinuities is proposed. Moreover, the quasilinear diffusion coefficient is shown to deviate significantly from the lowest order Larmor radius scaling vertical bar delta H vertical bar(2) proportional to v(perpendicular to)(2n), where delta H is the perturbed Hamiltonian. This is not only caused by the finite Larmor radius effects, but also by the inhomogeneous electric field polarization and by the changes to the guiding centre orbits during the wave-particle interactions.

  • 329.
    Johnson, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Salmi, A.
    Steinbrecher, G.
    Eriksson, L. -G
    Hellsten, T.
    Höök, Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Schneider, M.
    Library for RF Interactions in Orbit Following Codes2011In: RADIO FREQUENCY POWER IN PLASMAS: PROCEEDINGS OF THE 19TH TOPICAL CONFERENCE, 2011Conference paper (Refereed)
    Abstract [en]

    A new code-library has been developed to handle quasi-linear wave particle interactions in orbit following Monte Carlo codes, RFOF (RF interactions in Orbit Following codes). This library will enable a large number of orbit following codes to model fast ion acceleration during ICRF and Lower Hybrid heating. The RFOF consists of two main modules: one evaluates the resonance condition, the other the resulting RF acceleration. The resonance condition is tested at each step along the orbit and the location of the next upcoming resonance is predicted. When a particle reaches the resonance, a quasi-linear acceleration is calculated with a novel Monte Carlo technique that avoids the time-consuming evaluation of phase-space derivatives of the interaction strength. In RFOF the wave-particles interactions are assumed to be localized to a single point on the orbit. This is often valid for the ion cyclotron and lower hybrid frequency ranges, but prevents the treatment of bounce and precessional resonances. The RFOF has been developed within the European Task Force for Integrated Tokamak Modelling, enabling interaction between experts in different fields. As a result the code is designed with a simple and generic interface, with a minimum of assumptions on e.g. the geometry. Successful integration with the two orbit following codes, ASCOT and SPOT, has already been demonstrated.

  • 330. Jucker, M.
    et al.
    Graves, J. P.
    Cooper, W. A.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ion cyclotron resonance heating with consistent finite orbit widths and anisotropic equilibria2011In: PLASMA PHYS CONTROL FUSION, 2011, Vol. 53, no 5, p. 054010-Conference paper (Refereed)
    Abstract [en]

    Minority ion cyclotron resonance heating is studied using the self-consistent numerical model SCENIC. This model includes 3D geometries with full shaping and anisotropic pressure effects, warm contributions to the dielectric tensor and full orbit effects. It evolves the equilibrium, wave field and hot particle distribution function iteratively until a self-consistent solution is found. We will show applications to JET-like two-dimensional equilibria with minority heating scenarios. The effects due to different heating locations on the hot particle distribution function, the hot dielectric tensor and the equilibrium will be studied for symmetric wave injection. Finally, the RF-induced particle pinch is investigated using asymmetric wave injection.

  • 331. Jucker, M.
    et al.
    Graves, J. P.
    Cooper, W. A.
    Mellet, N.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunner, S.
    Integrated modeling for ion cyclotron resonant heating in toroidal systems2011In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 182, no 4, p. 912-925Article in journal (Refereed)
    Abstract [en]

    An integrated model capable of self-consistent Ion Cyclotron Resonant Heating (ICRH) simulations has been developed. This model includes both full shaping and pressure effects, warm contributions to the dielectric tensor, pressure anisotropy and finite orbit width. It evolves the equilibrium, wave field and full hot particle distribution function until a self-consistent solution is found. This article describes the workings of the three codes VMEC, LEMan and VENUS and how they are linked for iterated computations in a code package we have named SCENIC. The package is thoroughly tested and it is demonstrated that a number of iterations have to be performed in order to find a consistent solution. Since the formulation of the problem can treat general 3D systems, we show a quasi-axisymmetric stellarator low power test case, and then concentrate on experimentally relevant Joint European Torus (JET) 2D configurations.

  • 332. Kalupin, D.
    et al.
    Asunta, O.
    Coelho, R.
    Coster, D.
    Ferreira, J.
    Figueiredo, A.
    Gal, K.
    Ivanova-Stanik, I.
    Jonnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Owsiak, M.
    Palak, B.
    Schneider, M.
    Stankiewicz, R.
    Strand, P.
    Predictive simulations of reactor-scale plasmas fuelled with multiple pellets with the European Transport Simulator2015In: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Conference paper (Refereed)
  • 333. Kantor, M.
    et al.
    Tsalas, M.
    Litnovsky, A.
    Rudakov, D.
    Bozhenkov, S.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ashikawa, N.
    Pospieszczyk, A.
    Philipps, V.
    Characterization of dust particles in the TEXTOR tokamak with Thomson scattering diagnostic2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S711-S714Article in journal (Refereed)
    Abstract [en]

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

  • 334. Kaveeva, E.
    et al.
    Rozhansky, V.
    Tendler, Michael
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Interpretation of the observed radial electric field inversion in the TUMAN-3M tokamak during MHD activity2008In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 48, no 7Article in journal (Refereed)
    Abstract [en]

    A theoretical model for the toroidal rotation spin-up and generation of a positive radial electric field during the stochastization of plasma edge is put forward. Equations for the toroidal velocity and for modification of the core radial electric field have been derived. A detailed comparison of the model results with the radial electric field and plasma potential measurements during MHD activity in the TUMAN-3M tokamak is presented.

  • 335. Kaveeva, E.
    et al.
    Rozhansky, V.
    Tendler, Michael
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Mechanism of resonant magnetic perturbation screening2010In: 37th EPS Conference on Plasma Physics 2010, EPS 2010: Volume 2, 2010, p. 823-825Conference paper (Refereed)
  • 336. Kazakov, Ye. O.
    et al.
    Ongena, J.
    Wright, J. C.
    Wukitch, S. J.
    Lerche, E.
    Mantsinen, M. J.
    Van Eester, D.
    Craciunescu, T.
    Kiptily, V. G.
    Lin, Y.
    Nocente, M.
    Nabais, F.
    Nave, M. F. F.
    Baranov, Y.
    Bielecki, J.
    Bilato, R.
    Bobkov, V.
    Crombe, K.
    Czarnecka, A.
    Faustin, J. M.
    Felton, R.
    Fitzgerald, M.
    Gallart, D.
    Giacomelli, L.
    Golfinopoulos, T.
    Hubbard, A. E.
    Jacquet, Ph.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lennholm, M.
    Loarer, T.
    Porkolab, M.
    Sharapov, S. E.
    Valcarcel, D.
    Van Schoor, M.
    Weisen, H.
    Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating2017In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 13, no 10, p. 973-+Article in journal (Refereed)
  • 337. Kazakov, Ye O.
    et al.
    Pusztai, I.
    Fülöp, T.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Poloidal asymmetries due to ion cyclotron resonance heating2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 10, p. 105010-Article in journal (Refereed)
    Abstract [en]

    The poloidal density asymmetry of impurity ions in ion cyclotron resonance heated (ICRH) discharges is calculated. The link between the asymmetry strength and ICRH and plasma parameters is quantified. The main parameter governing the asymmetry strength is identified to be the minority ion temperature anisotropy. Through numerical simulations with the full-wave TORIC code coupled to the Fokker-Planck quasilinear solver SSFPQL, the dependence of the anisotropy on various parameters, such as ICRH power, background density and temperature, minority and impurity concentration and toroidal wavenumber has been investigated. An approximate expression for the poloidal asymmetry of impurities as a function of plasma parameters, resonance location and ICRH power is given. A quantification of the link of the impurity asymmetry and ICRH heating is valuable not only for understanding the changes in the cross-field transport but also for the possibilities to use the asymmetry measurements as diagnostics.

  • 338. Kazakov, Ye.O.
    et al.
    Fülöp, T.
    Pusztai, I.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Effect of plasma shaping and resonance location on minority ion temperature anisotropy in tokamak plasmas heated with ICRH2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 401, no 1, p. 012011-Article in journal (Refereed)
    Abstract [en]

    Poloidal asymmetries of the impurity distribution, which are observed in tokamaks, may influence the impurity cross-field transport. Low field side ion cyclotron resonance heating (ICRH) often results in an inboard accumulation of impurities, which may in turn lead to an outward convective impurity flux. The temperature anisotropy of the ICRH-heated minority ions is identified to be one of the main parameters governing the impurity asymmetry strength. In the present work we analyze the effect of plasma shaping and the ICRH resonance location on the minority temperature anisotropy by means of the TORIC-SSFPQL modelling. We find that ellipticity reduces the anisotropy level due to the wave defocussing and broader absorption regions for the elongated plasmas. The temperature anisotropy decrease in case of the resonance layers located closer to the edge is caused by the significant reduction in heating power densities due to geometrical reasons.

  • 339. Kazakov, Ye.O.
    et al.
    Fülöp, T.
    Pusztai, I.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Poloidal density asymmetries due to ion cyclotron resonance heating2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics, Volume 2, 2012, 2012, p. 894-897Conference paper (Refereed)
  • 340.
    Khan, Muhammad Waqas Mehmood
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Braking of Plasma Rotation by Non-axisymmetric Magnetic Fields in EXTRAP T2R2011In: Proceedings of the 38th European Physical Society Conference on Plasma Physics, 2011, p. 841-844Conference paper (Refereed)
  • 341. Kim, H T
    et al.
    Romanelli, M
    Yuan, X
    Kaye, S
    Budny, R
    Weisen, H
    Buchanan, J
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lupelli, I
    Statistical Validation of Transport Models on Baseline Discharges in Preparation for the Extrapolation to JET DT2016In: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Conference paper (Refereed)
  • 342. Kim, Hyun-Tae
    et al.
    Romanelli, M.
    Yuan, X.
    Kaye, S.
    Sips, A. C. C.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Buchanan, J.
    Statistical validation of predictive TRANSP simulations of baseline discharges in preparation for extrapolation to JET D-T2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 6, article id 066032Article in journal (Refereed)
    Abstract [en]

    This paper presents for the first time a statistical validation of predictive TRANSP simulations of plasma temperature using two transport models, GLF23 and TGLF, over a database of 80 baseline H-mode discharges in JET-ILW. While the accuracy of the predicted Te with TRANSP-GLF23 is affected by plasma collisionality, the dependency of predictions on collisionality is less significant when using TRANSP-TGLF, indicating that the latter model has a broader applicability across plasma regimes. TRANSP-TGLF also shows a good matching of predicted Ti with experimental measurements allowing for a more accurate prediction of the neutron yields. The impact of input data and assumptions prescribed in the simulations are also investigated in this paper. The statistical validation and the assessment of uncertainty level in predictive TRANSP simulations for JET-ILW-DD will constitute the basis for the extrapolation to JET-ILW-DT experiments.

  • 343. Kipitily, V.
    et al.
    Pinches, S.
    Sharapov, S. E.
    Alper, B.
    Howell, D.
    Cecil, F. C.
    Darrow, D.
    Goloborodko, V.
    Perez von Thun, C.
    Plyusnin, V.
    Smolyakov, A. I.
    Yavorskij, V.
    Gatu Johnson, M.
    Craciunescu, T.
    Hellesen, C.
    Johnson, T.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Liang, Y.
    Koslowski, H. R.
    Mailloux, J.
    Nabais, F.
    Reich, M.
    de Vries, P.
    Zoita, V. L.
    Studies of MHD Effects on Fast Ions: towards Burning Plasma with ITER-like Wall on JET2010Conference paper (Other academic)
  • 344. Kiptily, V. G.
    et al.
    Borba, D.
    Cecil, F. E.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Darrow, D.
    Goloborod'Ko, V.
    Hill, K.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Murari, A.
    Nabais, F.
    Pinches, S. D.
    Reich, M.
    Sharapov, S. E.
    Yavorskij, V.
    Chugunov, I. N.
    Gin, D. B.
    Gorini, G.
    Shevelev, A. E.
    Syme, D. B.
    Zoita, V.
    Fast ion JET diagnostics: Confinement and losses2008In: BURNING PLASMA DIAGNOSTICS, 2008, Vol. 988, p. 283-290Conference paper (Refereed)
    Abstract [en]

    A study of magnetically confined fast ions in tokamaks plays an important role in burning plasma research. To reach ignition and steady burning of a reactor plasma an adequate confinement of energetic ions produced by NBI heating, accelerated with ICRF and born in fusion reactions is essential to provide efficient heating of the bulk plasma. Thus, investigation of the fast ion behaviour is an immediate task for present-day large machines, such as JET, in order to understand the main mechanisms of slowing down, redistribution and losses, and to develop optimal plasma scenarios. Today's JET has an enhanced suite of fast ion diagnostics both of confined and lost ions that enable to significantly contribute to this important area of research. Fast ion populations of p, d, t, 3He and 4He, made with ICRF, NBI, and fusion reactions have been investigated in experiments on JET with sophisticated diagnostics in conventional and shear-reversed plasmas, exploring a wide range of effects. This paper will introduce to the JET fast-ion diagnostic techniques and will give an overview of recent observations. A synergy of the unique diagnostic set was utilised in JET, and studies of the response of fast ions to MHD modes (e.g. tornado modes, sawtooth crashes), fast 3He-ions behaviour in shear-reversed plasmas are impressive examples of that. Some results on fast ion losses in JET experiments with various levels of the toroidal field ripple will be demonstrated.

  • 345. Kiptily, V. G.
    et al.
    Gorini, G.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zoita, V. L.
    et al.,
    Doppler broadening of gamma ray lines and fast ion distribution in JET plasmas2010In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, no 8, p. 084001-Article in journal (Refereed)
    Abstract [en]

    The Doppler broadening of individual gamma-ray lines was measured with a high purity germanium detector in JET plasma experiments. High-resolution gamma-ray spectrometry of nuclear reactions between energetic D, He-3 and He-4 ions accelerated by ion cyclotron resonance heating and main plasma impurities such as carbon and beryllium has been used. The nuclear reactions giving rise to gamma-rays have been identified and an effective temperature of the heated ions has been obtained in JET discharges. This technique could be used for fast ion and fusion alpha-particle studies in ITER.

  • 346. Kiptily, V. G.
    et al.
    Van Eester, D.
    Lerche, E.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Mayoral, M-L
    Cecil, F. E.
    Darrow, D.
    Johnson, M. Gatu
    Goloborod'ko, V.
    Gorini, G.
    Hellesen, C.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lin, Y.
    Maslov, M.
    Nocente, M.
    Tardocchi, M.
    Voitsekhovitch, I.
    Fast ions in mode conversion heating (He-3)-H plasmas in JET2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 7, p. 074010-Article in journal (Refereed)
    Abstract [en]

    Fast ions were analysed in experiments focusing on fundamental He-3 minority and mode conversion (MC) in the ion cyclotron resonance range of frequencies (ICRF) in H plasmas and on second harmonic heating of He-3 ions at 2.65 T mimicking D-T plasma heating in ITER at half its nominal toroidal magnetic field. Gamma-ray spectrometry, neutral particle analysers and fast-ion loss diagnostics provided information on the generation of fast-ion populations and on the distribution of ICRH power among the species in various heating scenarios and for a large range of He-3 concentrations. In the scenario with the fundamental He-3 minority and MC wave heating at B-T(0) = 3.41 T and f approximate to 32 MHz, fast He-3 ions accelerated by ICRH in the MeV energy range were detected in discharges with low He-3 concentration. In the experiments with a He-3 concentration scan it was found that at a He-3 concentration of approximate to 2.2% the He-3 ion losses disappeared while a population of energetic D ions gradually built up due to a redistribution of the ICRH power between species on reaching the first MC regime. Under those conditions the ICRF-heated D beam ions effectively absorbed the wave power at their Doppler shifted resonance, which was close to the plasma centre. In discharges with second harmonic heating of He-3 ions at B-T(0) = 2.65 T and f approximate to 52 MHz, the confined energetic He-3 ions were found in the MeV energy range. There is some evidence that the D ions were also accelerated by ICRF. This paper also demonstrates that the synergy of the various fast ion diagnostics allows making a broad picture of the physics of the redistribution of the absorbed ICRH power in complicated heating scenarios of JET.

  • 347. Kiptily, V. G.
    et al.
    von Thun, C. P. P.
    Pinches, S. D.
    Sharapov, S. E.
    Borba, D.
    Cecil, F. E.
    Darrow, D.
    Goloborod'ko, V.
    Craciunescu, T.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nabais, F.
    Reich, M.
    Salmi, A.
    Yavorskij, V.
    Cecconello, M.
    Gorini, G.
    Lomas, P.
    Murari, A.
    Parail, V.
    Popovichev, S.
    Saibene, G.
    Sartori, R.
    Syme, D. B.
    Tardocchi, M.
    de Vries, P.
    Zoita, V. L.
    von Thun, C. P. Perez
    Recent progress in fast ion studies on JET2009In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, no 6Article in journal (Refereed)
    Abstract [en]

    This paper presents recent results on fast ion studies on JET. A set of diagnostics for both confined and lost fast ions was employed for investigating the response of fast ions to MHD modes and for studying their behaviour in plasmas with toroidal field ripple and in shear-reversed plasmas. A dependence of the losses on MHD mode amplitude was deduced from the experimental data. A study of various plasma scenarios has shown that a significant redistribution of the fast ions happens during changes in the profile of the safety factor from shear-reversed to monotonic. Significant changes in the losses of ICRH accelerated protons were found to be associated with L-H confinement transitions in plasmas. After an L-H transition, an abrupt decrease in the ICRH proton losses was observed. In plasmas with an internal transport barrier, the loss of ICRH accelerated ions was found to increase as the barrier forms. Further results concerning fast ion losses were obtained during JET experiments in which the magnitude of the TF ripple was varied. The ripple losses of fusion products appear similar to classical losses, and are in agreement with modelling.

  • 348. Kiptily, V.
    et al.
    Pinches, S. D.
    Sharapov, S. E.
    Borba, D.
    Cecil, F. E.
    Darrow, D.
    Goloborod’ko, V.
    Craciunescu, T.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nabais, F.
    Perez von Thun, C. P.
    Reich, M.
    Salmi, A.
    Yavorskij, V.
    Cecconello, M.
    Gorini, G.
    Lomas, P.
    Murari, A.
    Parail, V.
    Popovichev, S.
    Saibene, G.
    Satori, R.
    Syme, D. B.
    Tardocchi, M.
    de Vries, P.
    Zoita, V. L.
    Recent Progress in Fast-Ion Physics on JET2008Conference paper (Other academic)
  • 349. Kirschner, A.
    et al.
    Philipps, V.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Mertens, P.
    Overview of erosion mechanisms, impurity transport, and deposition in TEXTOR and related modeling2005In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 47, no 2, p. 146-160Article in journal (Refereed)
    Abstract [en]

    This paper gives an overview of the research activities at TEXTOR on impurity production, impurity transport through the plasma, and then deposition. First, laboratory experiments on chemical erosion by hydrogen and oxygen and radiation-enhanced sublimation are described, followed by the main part, which concentrates on the TEXTOR data of impurity release, impurity transport, and redeposition. The differences between the behavior of high-Z and low-Z materials are discussed. Many of the TEXTOR experiments are carried out using special limiter locks, but the overall carbon balance of net erosion sources and net deposition zones are also shown. Finally, modeling of erosion and dedicated transport experiments are addressed.

  • 350. Kirschner, Andreas
    et al.
    Kreter, Arkadi
    Wienhold, Peter
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Pospieszczyk, Albrecht
    Ding, R
    Borodin, Dmitriy
    Brezinsek, Sebastijan
    Sergienko, Gennady
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Linsmeier, Christian
    Modelling of deposition and erosion of injected WF6 and MoF6 in TEXTOR2016In: Nuclear Materials and Energy, ISSN 2352-1791Article in journal (Refereed)
    Abstract [en]

    Tracer injection experiments in TEXTOR with MoF 6 and WF 6 lead to local deposition of about 6% for Mo and about 1% for W relative to the injected amount of Mo and W atoms. Modelling of these experiments has been done with ERO applying updated data for physical sputtering. The dissociation of the injected molecules has been treated in a simplified manner due to the lack of dissociation rate coefficients. How- ever, with this it was possible to reproduce the observed radial penetration of Mo and W atoms into the plasma. The modelled local deposition efficiencies are about 50% for Mo and 60% for W assuming typical plasma parameters for the experimental conditions used. To reproduce the measured deposition efficien- cies an enhancement factor for the erosion of deposited Mo and W has to be assumed ( ∼10 for Mo and ∼25 for W). Due to the rather low electron temperature T e of these plasma conditions (T e ∼15 eV at the location of injection), Mo and W are mostly sputtered by impurities whereas sputtering due to deuterium is negligible. A parameter study applying larger electron temperature leads to increased sputtering and thus to reduced local deposition efficiencies of about 30% for Mo and 5% for W. Though, even under these conditions enhanced erosion, albeit with reduced enhancement factors, is needed in the modelling to obtain the small measured deposition efficiencies.

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