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  • 51.
    Hjelm, Mats
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Nilsson, H. -E
    Full band Monte Carlo simulation of cubic and hexagonal silicon carbide polytypes and devices2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, s. 61-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The GEMS (General Monte Carlo Semiconductor) simulator is a full band ensemble program developed at Mid-Sweden University. A principal objective of the project is to create a flexible tool that can be used for the exploration of properties of new semiconductor materials as well as devices fabricated of these materials. Both cubic and hexagonal crystal symmetries can be handled with the simulator, and any material with these symmetries can be simulated if an appropriate electronic band structure together with the parameters for the scattering mechanisms is provided. During the development of GEMS a large number of studies have been performed of bulk charge transport and device characteristics. The simulated materials are 2H-, 3C-, 4H- and 6H-SiC, as well as silicon. This presentation discusses the charge transport properties of the studied SiC polytypes, and the resulting performance of the simulated devices.

  • 52.
    Hållstedt, Julius.
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Parent, Arnaud
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Zhang, Shi-Li
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Östling, Mikael
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Radamson, Henry H.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Strain and electrical characterization of boron-doped SiGeC layers grown by chemical vapor deposition2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, s. 31-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Incorporation, induced strain and electrical properties of boron and carbon in Si1-x-yGexCy epitaxial layers (x = 0.23 and 0.28 with y = 0 and 0.005) grown by chemical vapour deposition (CVD) have been studied. The boron concentration in the epitaxial layers was in the range of 3 x 10(18)-1 x 10(21) cm(-3). The growth rate enhanced weakly by increasing boron partial pressure up to 0.002 mtorr ( corresponding to 2 x 10(19) cm(-3)) where a significant increase in deposition rate was observed. In SiGeC layers, the active boron concentration was obtained from the strain compensation amount. It was also found that the boron atoms have a tendency to locate at substitutional sites more preferentially compared to carbon. The incorporation of boron in SiGeC layers was clearly improved in the range 2 x 10(19)-3 x 10(20) cm(-3). These investigations also enabled an estimation of the Hall scattering factor of the SiGeC layers. A comparison between our results with the previous theoretical calculations showed a good agreement. This created the possibility to evaluate the drift mobility in our samples.

  • 53.
    Isheden, Christian
    et al.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Hellström, Per-Erik
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Radamson, Henry H.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Zhang, Shi-Li
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Östling, Mikael
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Selective Si etching using HCl vapor2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, s. 107-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selective Si etching using HCl in a reduced pressure chemical vapor deposition reactor in the temperature range 800-1000 degrees C is investigated. At 900 degrees C, the etch process is anisotropic, exhibiting the densely packed (100), (311) and (111) surfaces. This behavior indicates that the etch process is limited by surface reaction, since the etch rate in the directions with higher atomic concentration is lower. When the temperature is decreased to 800 degrees C, etch pits occur. A more isotropic etch is obtained at 1000 degrees C, however at this temperature the masking oxide is attacked and the etch surface is rough. Thus the temperature has to be confined to a narrow window to yield desirable properties under the present process conditions.

  • 54.
    Ivanova, Darya
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    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 layers2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014006-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 55.
    Ivanova, Darya
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Widdowson, A.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Likonen, J.
    Marot, L.
    Alves, E.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Pintsuk, G.
    An overview of the comprehensive First Mirror Test in JET with ITER-like wall2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014011-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 56. Jacob, Wolfgang
    et al.
    Linsmeier, Christian
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    13th International Workshop on Plasma-Facing Materials and Components for Fusion Applications/1st International Conference on Fusion Energy Materials Science2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 011001-Artikkel i tidsskrift (Annet vitenskapelig)
  • 57.
    Janson, Martin S.
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Linnarsson, Margareta K.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Hallén, Anders
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Svensson, Bengt G.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Achtziger, N.
    Uneus, L.
    Spetz, A. Lloyd
    Forsberg, U.
    Hydrogen in the wide bandgap semiconductor silicon carbide2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T108, s. 99-112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we give a review of our recent results related to the incorporation of hydrogen (H) in silicon carbide (SiC) and its interaction with acceptor doping atoms and implantation induced defects. Hydrogen is an abundant impurity in the growth of epitaxial SiC since it is present in the precursor gases and since H-2 is used as the carrier gas. High concentrations of hydrogen are indeed incorporated into highly doped p-type epi-layers and it is shown that the main source is the carrier gas. Furthermore, it is revealed that the entire substrate becomes homogeneously filled with hydrogen during growth and that this hydrogen is more thermally stable than that in the epi-layer. Incorporation of hydrogen from an H-2 ambient, at temperatures considerably lower than those used for epitaxy, is also demonstrated in p-type samples coated with a catalytic metal film. This effect is most likely the cause for the increased series resistance observed in p-type SiC Schottky sensor devices using a catalytic metal gate after annealing at 600 degrees C in a H-2 containing ambient. Hydrogen is found to passivate the acceptors Al and B by forming electrically neutral H-acceptor complexes. Unlike in Si and GaAs, the two H-acceptor complexes in SiC exhibit very different dissociation energies, suggesting that the atomic configurations of the complexes are significantly different. The migration of mobile hydrogen in the presence of externally applied, or internal built-in, electric fields further reveals that hydrogen is present as H+ in p-type SiC. Finally, the redistribution and subsequent out-diffusion of low energy implanted H-1 and H-2 is investigated. Two annealing phases for the redistribution are observed, and the activation energies for the processes are extracted.

  • 58. Kahniashvili, Tina
    et al.
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Tevzadze, Alexander G.
    The evolution of primordial magnetic fields since their generation2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, nr 10, artikkel-id 104008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the evolution of primordial magnetic fields in an expanding cosmic plasma. For this purpose we present a comprehensive theoretical model to consider the evolution of MHD turbulence that can be used over a wide range of physical conditions, including cosmological and astrophysical applications. We model different types of decaying cosmic MHD turbulence in the expanding Universe and characterize the large-scale magnetic fields in such a medium. Direct numerical simulations of freely decaying MHD turbulence are performed for different magnetogenesis scenarios: magnetic fields generated during cosmic inflation as well as electroweak and QCD phase transitions in the early Universe. Magnetic fields and fluid motions are strongly coupled due to the high Reynolds number in the early Universe. Hence, we abandon the simple adiabatic dilution model to estimate magnetic field amplitudes in the expanding Universe and include turbulent mixing effects on the large-scale magnetic field evolution. Numerical simulations have been carried out for non-helical and helical magnetic field configurations. The numerical results show the possibility of inverse transfer of energy in magnetically dominated non-helical MHD turbulence. On the other hand, decay properties of helical turbulence depend on whether the turbulent magnetic field is in a weakly or a fully helical state. Our results show that primordial magnetic fields can be considered as a seed for the observed large-scale magnetic fields in galaxies and clusters. Bounds on the magnetic field strength are obtained and are consistent with the upper and lower limits set by observations of extragalactic magnetic fields.

  • 59. Kalinina, E.
    et al.
    Onushkin, G.
    Strel'chuk, A.
    Davidov, D.
    Kossov, V.
    Yafaev, R.
    Hallén, Anders.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Kuznetsov, A.
    Konstantinov, A.
    Characterization of Al-implanted 4H SiC high voltage diodes2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 207-210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of 4H-SiC chemical vapor deposition epitaxial layers were studied by different methods. The effects of structural defects in 4H-SiC epitaxial layers on electrical and luminescence properties of Al high dose ion implanted p(+)-n junctions were studied. It has been shown that the structural imperfections of low-doped layers affect some electrical characteristics of the ion doped p(+)-n junctions created in these epitaxial layers.

  • 60.
    Karlsson, Tomas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Axnäs, Ingvar
    On enhanced aurora and low-altitude parallel electric fields2005Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, nr 5, s. 419-422Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Enhanced auroras are bands of enhanced intensity, sometimes observed along the bottom edges of auroral arcs. It is here proposed that they sometimes are due to local electron energization by low-altitude. downward-directed DC electric fields. which arise as a consequence of the ionospheric response to small-scale auroral current systems. Simulations of such structures are presented. and the electron energization mechanism is discussed. The enhanced auroras would, in this model, appear parallel and close to (perhaps only a few kin front) an ordinary auroral arc. Detailcd 3-D observations of auroral arc structures could resolve if enhanced auroras sometimes take this form.

  • 61.
    Koivisto, Tomi S.
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Helsinki University, Finland; Stockholm University, Sweden.
    Nyrhinen, Hannu J.
    Stability of disformally coupled accretion disks2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 92, nr 10, artikkel-id 105301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The no-hair theorem postulates that the only externally observable properties of a black hole are its mass, its electric charge, and its angular momentum. In scalar-tensor theories of gravity, a matter distribution around a black hole can lead to the so called 'spontaneous scalarisation' instability that triggers the development of scalar hair. In the Brans-Dicke type theories, this effect can be understood as a result of tachyonic effective mass of the scalar field. Here we consider the instability in the generalised class of scalar-theories that feature non-conformal, i.e. 'disformal', couplings to matter. Such theories have gained considerable interest in the recent years and have been studied in a wide variety of systems, both cosmological and astrophysical. In view of the prospects of gravitational wave astronomy, it is relevant to explore the implications of the theories in the strong-gravity regime. In this article, we concentrate on the spontaneous scalarisation of matter configurations around Schwarzschild and Kerr black holes. We find that in the more generic scalar-tensor theories, the instability of the Brans-Dicke theory can be enhanced, suggesting violations of the no-hair theorem. On the other hand, we find that, especially if the coupling is very strong, or if the gradients in the matter distribution are negligible, the disformal coupling tends to stabilise the system.

  • 62.
    Koivisto, Tomi S.
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Urban, Federico R.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Université Libre de Bruxelles, Belgium.
    Doubly-boosted vector cosmologies from disformal metrics2015Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, nr 9, artikkel-id 095301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A systematic dynamical system approach is applied to study the cosmology of anisotropic Bianchi I universes in which a vector field is assumed to operate on a disformal frame. This study yields a number of new fixed points, among which are anisotropic scaling solutions. Within the simplifying assumption of (nearly) constant-slope potentials these are either not stable attractors, do not describe accelerating expansion or else they feature too large anisotropies to be compatible with observations. Nonetheless, some solutions do have an appeal for cosmological applications in that isotropy is retained due to rapid oscillations of the vector field. Such cosmological scenarios could describe physics beyond standard model such as extra dimensional models that predict disformal couplings between vector and scalar fields.

  • 63. Koivuranta, S.
    et al.
    Likonen, J.
    Hakola, A.
    Coad, J. P.
    Widdowson, A.
    Hole, D. E.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Post-mortem measurements of fuel retention at JET2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014052-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The deuterium inventory at Joint European Torus in co-deposits and bulk material in inner, outer and upper wall components of the vacuum vessel exposed in 2007-2009 has been determined using nuclear reaction analysis and secondary ion mass spectrometry and optical microscopy. Approximately 1.8 g of the deuterium is retained in these areas, which corresponds to similar to 0.07% of the retained deuterium.

  • 64. 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 experiments2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014069Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 65. Krieger, K.
    et al.
    Sieglin, B.
    Balden, M.
    Coenen, J. W.
    Goeths, B.
    Laggner, F.
    de Marne, P.
    Matthews, G. F.
    Nille, D.
    Rohde, V.
    Dejarnac, R.
    Faitsch, M.
    Giannone, L.
    Herrmann, A.
    Horacek, J.
    Komm, M.
    Pitts, R. A.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Thorén, E.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tolias, P.
    Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014030Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II system. The exposed sample was designed with an elevated sloped surface inclined against the incident magnetic field to increase the projected parallel power flux to a level were transient melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point to the sample location. As extension to previous melt studies in the new experiment both the current flow from the sample to vessel potential and the local surface temperature were measured with sufficient time resolution to resolve individual ELMs. The experiment provided for the first time a direct link of current flow and surface temperature during transient ELM events. This allows to further constrain the MEMOS melt motion code predictions and to improve the validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved samples confirms the decreased melt motion observed at shallower magnetic field line to surface angles compared to that at leading edges exposed to the parallel power flux.

  • 66. Lehnert, B.
    et al.
    Scheffel, Jan
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    On the minimum elementary charge of an extended electromagnetic theory2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 65, nr 3, s. 200-207Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Steady axisymmetric equilibria of an earlier developed extended electromagnetic theory are considered. as based on a nonzero electric field divergence in the vacuum state and Lorentz invariance. The general solutions are derived from a generating function which yields electrically charged particle-like states when its radial part diverges at the origin. For a corresponding electron model, the integrated charge, magnetic moment, mass (energy), and angular momentum still become nonzero and finite, provided that the characteristic radius is made to shrink to that of a point-charge-like state. This removes the problem of an infinite self-energy, and presents a possible alternative to the conventional renormalization process. With the subsidiary quantum conditions on magnetic moment, angular momentum, and magnetic flux. a variational analysis is applied to find an extremum of the electronic charge. The resulting minimum value deviates only by about 3 percent from that of the experimentally determined elementary charge, and it depends only on the velocity of light and Planck's constant. This indicates that the electronic charge may no longer be considered as an independent constant of nature. but can be deduced in terms of these two constants. There could be several possible explanations of the obtained deviation, of which the most probable appears to be due to refinements caused by quantization of the field equations already from the outset.

  • 67.
    Lehnert, Bo
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Boundary conditions and spin of a dense light beam2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 74, nr 1, s. 139-144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A light beam of high photon density and spatially limited cross-section is analysed with respect to its boundary conditions and angular momentum ( spin). For Maxwell's equations in a vacuum state of vanishing electrical field divergence, the exact solutions are found not to be reconcilable with a beam having a limited cross-section and a nonzero spin. Transverse spatial beam derivatives only become possible as an approximation when their characteristic lengths are very large as compared to the relevant wavelengths, but even then there is no spin. A revised electromagnetic theory, based on a nonzero electric field divergence in the vacuum state, leads on the other hand to beam configurations for which there can exist strong transverse derivatives in a boundary region, as well as a nonzero spin. The Poynting vector then has components both in the axial direction of propagation and in the transverse direction along the boundary. The angular momentum, being imagined as an equivalent sum of momenta of the individual photons in the beam interior, is then replaced by a real spin generated and localized in the boundary layer.

  • 68.
    Lehnert, Bo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Half a century of fusion research towards ITER2013Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, nr 1, s. 018201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A review is given on plasma physics and controlled thermonuclear fusion research since the late 1950s and up to the present day. Special emphasis is given to various proposed magnetic plasma confinement systems, as well as to the research aiming at the planned International Thermonuclear Experimental Reactor (ITER) project. The latter is based on the tokamak field geometry of a strong toroidal magnetic field, combined with an inductively imposed toroidal plasma current. Experimental and theoretical research has been conducted on the fundamental problems of confinement, equilibrium, stability, plasma transport and plasma heating. During this development two milestones have been passed on the way to ITER, namely the removed threat by Bohm diffusion at the end of the 1960s, and the discovery of the High Mode at the beginning of the 1980s. Finally, some future perspectives are shortly given on this line of research.

  • 69.
    Lehnert, Bo
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Screw-shaped light in extended electromagnetics2005Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, nr 5, s. 359-365Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Twisted light beams have recently been observed for which the energy travels ill a corkscrew-shaped path. spiralling around the beam's central axis. These discoveries arc expected to become important to the development of new methods in the field of communication. as well as to the invention of new tools in microbiology. In this paper is shown that conventional theory based oil Maxwell's equations cannot explain the basic features of twisted light. On the other hand an extended electromagnetic theory, based oil a nonzero electric field divergence in the vacuum state. appears to be reconcilable with the main behaviour of the twisted light phenomena. The solutions and the set of modes being obtained from this extended theory are applicable both to models of high and low density photon beams and to those of individual photons. all having limited extensions in space and possessing an angular momentum (spin). Thereby beam models call be developed the intensity of which forms a ring-shaped cross-section, and individual photon models call be obtained which have the features of "needle radiation". However. within the limits of validity of the approximations made so far in the analysis. it is not clear whether the effective diameter of the individual photon models call he small enough to approach atomic dimensions.

  • 70.
    Lehnert, Bo
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    The electron as a steady-state confinement system2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T113, s. 41-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An extended Lorentz invariant electromagnetic theory includes the additional degree of freedom provided by a nonzero electric charge density and an associated electric field divergence in the vacuum state. The theory is applied to an electron model of a steady electromagnetic state. Three new physical features come out of this analysis. First, a steady equilibrium can be established, by which the electron is prevented from "exploding" under the action of its self-charge, as otherwise being predicted by conventional theory. Second, a variational analysis with imposed subsidiary quantum conditions ends up in a parameter range where the deduced charge becomes nearly equal to the experimentally determined elementary charge. Independently of this, the radial balance of forces in the equilibrium state leads to a value of the charge in the same range, thereby deviating by only one percent from the experimental one. Third, this deviation may possibly become removed by a quantum mechanical correction. If this would come out to be true, the elementary free charge would no longer remain an independent constant of nature, but becomes determined by the velocity of light, Planck's constant, and the dielectric constant only.

  • 71. Likonen, J.
    et al.
    Airila, M.
    Alves, E.
    Barradas, N.
    Brezinsek, S.
    Coad, J. P.
    Devaux, S.
    Groth, M.
    Gruenhagen, S.
    Hakola, A.
    Jachmich, S.
    Koivuranta, S.
    Makkonen, T.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Strachan, J.
    Stamp, M.
    Widdowson, A.
    Deposition of (13)C tracer in the JET MkII-HD divertor2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Migration of (13)C has been investigated at JET by injecting (13)C-labelled methane at the outer divertor base at the end of the 2009 campaign. The (13)C deposition profiles on carbon fibre composite divertor tiles were measured by secondary ion mass spectrometry and Rutherford backscattering techniques. (13)C was mainly deposited near the puffing location on the outer divertor base tiles. High amounts of (13)C were also found at the outer vertical target: at the bottom of the lower and at the top of the upper plates. Thirty-three percent of puffed (13)CH(4) was instantly pumped out by the divertor cryopump, which is close to the pump duct entrance. Global (13)C transport in the torus was modelled by the EDGE2D/EIRENE and DIVIMP codes, and local (13)C migration in the vicinity of the injection location by the ERO code. The DIVIMP and EDGE2D simulations show strong prompt deposition of (13)C directly adjacent to the injection point as well as in the far scrape-off layer (SOL) along both the inner and outer divertor targets. In addition, the measured (13)C deposition along the outer divertor wall tiles is qualitatively reproduced. However, EDGE2D and DIVIMP do not predict any deposition along the divertor surfaces facing the private plasma on the inner floor tile and inboard of the outer strike point on tile 5. The ERO calculations also indicate that most of the deposition occurs close to the injection location on the vertical face of the LBSRP tile and the horizontal part of tile 6.

  • 72. Likonen, J.
    et al.
    Alves, E.
    Baron-Wiechec, A.
    Brezinsek, S.
    Coad, J. P.
    Hakola, A.
    Heinola, K.
    Koivuranta, S.
    Matthews, G. F.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stan-Sion, C.
    Widdowson, A.
    First results and surface analysis strategy for plasma-facing components after JET operation with the ITER-like wall2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014016-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During the carbon wall operations of JET since 2001, an extensive post-mortem analysis programme has been carried out under the JET Task Force Fusion Technology and a similar analysis programme is underway for the JET-ILW tiles removed during the 2012 shutdown. The first post-mortem results from the JET ITER-like wall tiles have shown that the overall amount of deposition on the divertor tiles and on remote divertor areas has been reduced by more than an order of magnitude with respect to JET-C. In addition, the obtained data indicate a possible interaction between Be and W such as the formation of mixed Be-W layers. This could be due to the surface roughness of the tiles, or could be caused by diffusion or even alloying. Ion-beam analyses and secondary ion mass spectrometry techniques give only elemental information, so other techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, secondary electron microscopy/energy dispersive x-ray spectroscopy and nuclear microprobing are required. Since the nature of deposition and erosion has changed during the JET-ILW operations, a change in the post-mortem analysis programme is needed. For example, no cross-sectional samples from the sloping parts of tiles 4 and 6 are required. A strategy for post-mortem analyses of the marker-coated tiles will be presented in this paper.

  • 73.
    Lim, Jang-Kwon
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik.
    Bakowski, M.
    Analysis of 1.2 kV SiC buried-grid VJFETs2010Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T140, s. 014008-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    1.2 kV buried-grid vertical 4H-SiC JFET structures with normally-on (N-on) and normally-off (N-off) designs were investigated by simulation. The static and dynamic characteristics of the devices were determined over a wide range of current, voltage and gate drive conditions in the temperature range -50 degrees C to 250 degrees C. In this paper, the properties of the N-on designs with threshold voltages (V-th) -50 and -10 V are compared with the properties of the N-off design (V-th = 0). For constant V-th, on-resistance decreases and output current increases with increasing channel doping and decreasing channel width. Simulations show that an on-resistance lower than 2 m Omega cm(2) at 250 degrees C can be obtained provided the channel width is smaller than 1.5 and 0.5 mu m for N-on JFETs with V-th = -50 V and V-th = -10 V, respectively, and lower than 3 m Omega cm(2) provided the channel width is smaller than 0.3 mu m for the N-off JFET. At the same time, E-on decreases and E-off increases with increased channel doping concentration and reduced channel width. It is shown that E-on decreases with increasing channel doping concentration due to the reduced channel resistance for the faster turn-on process. E-off increases with increasing channel doping concentration due to the increase in gate-drain capacitance, C-GD.

  • 74. Lindberg, AC
    et al.
    Hellberg, Per-Erik
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Mohadjeri, B
    Zhang, Shi-Li
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Östling, Mikael
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Influence of interface roughness on electrical properties of pMOSFETs with a Si/Si1-xGex channel2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 22-25Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The effect of epitaxial growth induced surface roughness on the electrical properties of Si/Si1-xGex channel pMOSFETs was investigated. Grown by chemical vapour deposition for selective epitaxy, the surface of the channel region was considerably rougher for the channel structures with a buried Si1-xGex layer with x = 0.16-0.20 than for those with only Si. Although the increased surface roughness, determined by means of atomic force microscopy, resulted in a doubled interface charge density the density remained low at the mid-10(10) cm(-2) eV(-1) level. Furthermore, identical transconductance values were found for the MOSFETs with and without the Si1-xGex layer. Since the inversion charge was confined predominantly within the surface Si layer, the surface roughness apparently had little effect on the transconductance. However the subthreshold slope was found to increase from 78 mV/decade for the Si-only channel MOSFEF to 105 mV/decade for the Si/Si1-xGex channel MOSFETs.

  • 75.
    Lindblad, Göran
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Foundations of quantum mechanics?2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 84, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Does quantum mechanics have unsolved foundational problems? Is there a dividing line between the quantum and classical descriptions of the world? In this paper, I give an elementary introduction to the mathematical aspects of quantum and classical models which have prompted such questions.

  • 76.
    Linnros, Jan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Badel, Xavier
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Halvledarmaterial, HMA.
    Kleimann, Pascal
    Macro pore and pillar array formation in silicon by electrochemical etching2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, s. 72-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrochemical etching may be used to form high aspect-ratio pores and pillars in silicon. Starting from lithographically patterned surfaces, regular arrays of macro pores or pillars can be fabricated. The pitch and pillar) pore size must then scale with the depletion width, in turn set by the material resistivity. We review various results where the achievable pore diameter ranges from 100 mu m for high resistivity material to the submicron range for highly doped wafers. At slightly higher current density and using different patterns, pillars or walls may be formed. The fabricated structures may be further processed and we demonstrate oxidation, uniform wall doping and finally, filling of the structures to result in functional materials. Applications include both optical, microelectronic, material and bio-applications.

  • 77. Loarer, T.
    et al.
    Pecquet, A. -L
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    15th international conference on plasma-facing materials and components for fusion applications2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 010301Artikkel i tidsskrift (Fagfellevurdert)
  • 78. Loewenhoff, Thorsten
    et al.
    Wirtz, Marius
    Linke, Jochen
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    14th International Conference on Plasma-Facing Materials and Components for Fusion Applications Foreword2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 010301-Artikkel i tidsskrift (Fagfellevurdert)
  • 79. Lundin, P.
    et al.
    Gurell, J.
    Mannervik, S.
    Royen, P.
    Norlin, Lars-Olov
    KTH, Skolan för teknikvetenskap (SCI), Fysik. KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Hartman, H.
    Hibbert, A.
    Metastable levels in ScII: lifetime measurements and calculations2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 78, nr 1, s. 015301-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The lifetime of the metastable level 3d(21)G(4) in a singly charged scandium has been experimentally investigated at the ion storage ring CRYRING. A laser probing technique has been used for the studies. We also report calculated lifetimes and transition rates for 10 metastable levels in Sc II, including the 3d(21)G(4) state, by calculations using configuration interaction wave functions. The lifetime of the (1)G(4) level is experimentally determined to be tau(exp) = 2.64 +/- 0.18 s and is in good agreement with the theoretical calculation tau(th) = 2.84 s.

  • 80. Lungu, C. P.
    et al.
    Mustata, I.
    Zaroschi, V.
    Lungu, A. M.
    Anghel, A.
    Chiru, P.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Coad, P.
    Matthews, G. F.
    Beryllium coatings on metals for marker tiles at JET: development of process and characterization of layers2007Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T128, s. 157-161Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Preparatory study for the operation of the JET tokamak with a full metal wall (ITER-like wall project) also comprises several activities aiming at the development of thin beryllium coatings. The purpose is 2-fold: ( i) to coat Inconel (R) tiles of the inner wall cladding; (ii) to develop methods for production of films for so-called marker tiles in order to enable monitoring of Be erosion from limiters. Properties of the marker film must match, as closely as possible, those of bulk Be. The first step in the R&D process was to assess coating methods and the quality of layers deposited on test coupons. Smooth, dense Be films of high purity and good adhesion to the substrate were deposited with an average deposition rate of 5 +/- 0.5 nm s(-1) to a thickness of 7.5 mu m. A marker structure consisting of a 7.5 mu m Be film on top of a 2.5 mu m Ni interlayer deposited on a bulk Be block has been developed and characterized by means of material analysis methods. An overview of manufacturing processes and properties of the marker coatings is presented.

  • 81. Mannervik, S
    et al.
    Ellmann, A
    Lundin, P
    Norlin, Lars-Olov
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rostohar, D
    Royen, P
    Schef, P
    Lifetime measurements by laser probing in CRYRING - Recent experimental developments2005Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T119, s. 49-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A laser probing technique for lifetime measurements of long- lived metastable levels has been developed at the ion storage ring CRYRING. The method has been in use for about eight years and it has been applied to various ions. Levels with radiative lifetimes from a few milliseconds up to 28 s have been measured. The method has been continuously developed and this article is focused on recent experimental developments of the method in order to widen its applicability and to increase its efficiency and accuracy.

  • 82.
    Marklund, Göran T.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Figueiredo, Sonia
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Johansson, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Andre, M.
    Buchert, S.
    Kistler, L. M.
    Dynamics and characteristics of electric-field structures in the auroral return current region observed by Cluster2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T122, s. 34-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The temporal evolution and other characteristics of intense quasi- static electric fields in the return current region are discussed using Cluster observations. A narrow- scale, divergent electric field, the high- altitude signature of a positive U- shaped potential structure, was observed at the poleward edge of the central plasma sheet, close to magnetic midnight at a geocentric distance of about 4.2 Earth radii. Its acceleration potential increased from less than 1 to 3 kV on a 100 s timescale, similar to the formation time for ionospheric plasma density holes, and consistent with previous results for this kind of structure. In the adjacent upward current region, an energy decrease in inverted- V ions was observed some minutes prior to this. The inverted- V potential decrease was roughly equal to the subsequent perpendicular potential increase in the return current region, suggesting that a potential redistribution took place between the two adjacent current branches. Other characteristics of this and three other return current structures are summarized, to illustrate both common and different features of these. The structures are characterized by ( all values have been mapped to the ionospheric level) peak electric- field magnitudes of approximate to 1Vm(-1), bipolar or unipolar profiles, occurrence at plasma boundaries associated with plasma density gradients, perpendicular scale sizes of approximate to 10 km, downward field-aligned currents of approximate to 10 mu A m(-2), and upward electron beams with characteristic energies of a few hundred to a few thousand eV. The bipolar and unipolar electric- field profiles are proposed to reflect whether plasma populations, dense enough to support upward field-aligned currents (by which the return current can close) exist on both sides, or on one side only of the boundary.

  • 83. Masuzakil, S.
    et al.
    Tokitanii, M.
    Otsuka, T.
    Oya, Y.
    Hatan, Y.
    Miyamoto, M.
    Sakamoto, R.
    Ashikawa, N.
    Sakurada, S.
    Uemura, Y.
    Azuma, K.
    Yumizurus, K.
    Oyaizu, M.
    Suzuki, T.
    Kurotaki, H.
    Hamaguchi, D.
    Isobel, K.
    Asakura, N.
    Widdowson, A.
    Heinola, K.
    Jachmich, S.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Analyses of microstructure, composition and retention of hydrogen isotopes in divertor tiles of JET with the ITER-like wall2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014031Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results of the comprehensive surface analyses of divertor tiles and dusts retrieved from JET after the first ITER-like wall campaign (2011-2012) are presented. The samples cored from the divertor tiles were analyzed. Numerous nano-size bubble-like structures were observed in the deposition layer on the apron of the inner divertor tile, and a beryllium dust with the same structures were found in the matter collected from the inner divertor after the campaign. This suggests that the nano-size bubble-like structures can make the deposition layer to become brittle and may lead to cracking followed by dust generation. X-ray photoelectron spectroscopy analyses of chemical states of species in the deposition layers identified the formation of beryllium-tungsten intermetallic compounds on an inner vertical tile. Different tritium retention profiles along the divertor tiles were observed at the top surfaces and at deeper regions of the tiles by using the imaging plate technique.

  • 84. Matthews, G. F.
    et al.
    Beurskens, M.
    Brezinsek, S.
    Groth, M.
    Joffrin, E.
    Loving, A.
    Kear, M.
    Mayoral, M-L
    Neu, R.
    Prior, P.
    Riccardo, V.
    Rimini, F.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sips, G.
    Villedieu, E.
    de Vries, P.
    Watkins, M. L.
    JET ITER-like wall-overview and experimental programme2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports the successful installation of the JET ITER-like wall and the realization of its technical objectives. It also presents an overview of the planned experimental programme which has been optimized to exploit the new wall and other JET enhancements in 2011/12.

  • 85. Matthews, G. F.
    et al.
    Edwards, P.
    Hirai, T.
    Kear, M.
    Lioure, A.
    Lomas, P.
    Loving, A.
    Lungu, C.
    Maier, H.
    Mertens, P.
    Neilson, D.
    Neu, R.
    Pamela, J.
    Philipps, V.
    Piazza, G.
    Riccardo, V.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ruset, C.
    Villedieu, E.
    Way, M.
    Overview of the ITER-like wall project2007Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T128, s. 137-143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Work is in progress to completely replace, in 2008/9, the existing JET CFC tiles with a configuration of plasma facing materials consistent with the ITER design. The ITER-like wall (ILW) will be created with a combination of beryllium ( Be), tungsten ( W), W-coated CFC and Be-coated inconel tiles, with the material depending on the local anticipated heat flux and geometry. It is part of an integrated package of JET enhancements whose aim is to develop an understanding of the ITER materials issues and develop the techniques required to operate with inductive and advanced scenarios as close as possible to ITER parameters. Over 4000 tiles will be replaced and the ILW will accommodate additional heating up to at least 50 MW for 10 s. This paper describes the scientific background to the project, the technical objectives, the material configuration selected, the R&D behind the practical realization of the objectives and the generic problems associated with the Be tiles ( power handling capacity and disruption induced eddy currents). One of the objectives is to maintain or improve the existing CFC tile power handling performance which has been achieved in most cases by hiding bolt holes, optimizing tile size and profile and introducing castellations on plasma facing surfaces.

  • 86. Mayer, M.
    et al.
    Krat, S.
    Van Renterghem, W.
    Baron-Wiechec, A.
    Brezinsek, S.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Coad, P.
    Gasparyan, Y.
    Heinola, K.
    Likonen, J.
    Pisarev, A.
    Ruset, C.
    De Saint-Aubin, G.
    Widdowson, A.
    Erosion and deposition in the JET divertor during the first ILW campaign2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014051Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Erosion and deposition were studied in the JET divertor during the first JET ITER-like wall campaign 2011 to 2012 using marker tiles. An almost complete poloidal section consisting of tiles 0, 1, 3, 4, 6, 7, 8 was studied. The data from divertor tile surfaces were completed by the analysis of samples from remote divertor areas and from the inner wall cladding. The total mass of material deposited in the divertor decreased by a factor of 4-9 compared to the deposition of carbon during all-carbon JET operation before 2010. Deposits in 2011 to 2012 consist mainly of beryllium with 5-20 at.% of carbon and oxygen, respectively, and small amounts of Ni, Cr, Fe and W. This decrease of material deposition in the divertor is accompanied by a decrease of total deuterium retention inside the JET vessel by a factor of 10 to 20. The detailed erosion/deposition pattern in the divertor with the ITER-like wall configuration shows rigorous changes compared to the pattern with the all-carbon JET configuration.

  • 87.
    Menmuir, Sheena
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Impurity identifications, concentrations and particle fluxes from spectral measurements of the EXTRAP T2R plasma2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 74, nr 4, s. 439-448Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An absolute intensity calibrated 0.5m spectrometer with optical multi-channel analyser detector was used to observe the visible-UV radiation from the plasma in the EXTRAP T2R reversed field pinch experiment. Spectral lines were identified indicating the presence of oxygen, chromium, iron and molybdenum impurities in the hydrogen plasma. Certain regions of interest were examined in more detail and at different times in the plasma discharge. Impurity concentration calculations were made using the absolute intensities of lines of OIV and OV measured at 1-2 ms into the discharge generating estimates of the order of 0.2% of ne in the central region rising to 0.7% of ne at greater radii for OIV and 0.3% rising to 0.6% for OV. Edge electron temperatures of 0.5-5 eV at electron densities of 5-10 x 10(11) cm(-3) were calculated from the measured relative intensities of hydrogen Balmer lines. The absolute intensities of hydrogen lines and of multiplets of neutral chromium and molybdenum were used to determine particle fluxes (at 4-5 ms into the plasma) of the order 1 x 10(16), 7 x 1013 and 3 x 10(13) particles cm(-2) s(-1), respectively.

  • 88. Moser, L.
    et al.
    Marot, L.
    Steiner, R.
    Newman, M.
    Widdowson, A.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Likonen, J.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Pintsuk, G.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Meyer, E.
    Plasma cleaning of beryllium coated mirrors2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014069Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cleaning systems of metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Currently, plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). This work presents the results of plasma cleaning of rhodium and molybdenum mirrors exposed in JET-ILW and contaminated with typical tokamak elements (including beryllium and tungsten). Using radio frequency (13.56 MHz) argon or helium plasma, the removal of mixed layers was demonstrated and mirror reflectivity improved towards initial values. The cleaning was evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis.

  • 89. Mulot, M.
    et al.
    Anand, Srinivasan
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Carlstrom, C. F.
    Swillo, Marcin
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Taineau, A.
    Dry etching of photonic crystals in InP based materials2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 106-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photonic crystal (PC) etching in InP/GaInAsP using two different processes, namely Ar/CH4/H-2 based Reactive Ion Etching (RIE) and Ar/Cl-2 based Chemically Assisted Ion Beam Etching (CAIBE), is investigated in detail and the results are compared. Our goal was to identify the limits of the processes and to optimize process parameters for PC etching. With Ar/CH4/H-2 RIE, we obtained PC holes with smooth profiles. However, the etch depth depends strongly on the hole diameter; the smaller the hole diameter, the smaller is the obtained hole depth. This together with the obtained hole profiles indicates the presence of an etch-limiting mechanism and is attributed to inefficient removal of etch-products. In the case of Ar/Cl-2 CAME, we find that both shape and depth of the holes, depend on sample temperature, Cl-2 flow and etching duration. By optimizing the process parameters, we show that it is possible to balance the physical and chemical components in the etch process. We demonstrate that Ar/Cl-2 CAME is a promising process for PC etching in InP. With this process, we can obtain sufficiently deep holes (2.3-2.5 mum) even for hole diameters as small as 220nm.

  • 90. Möller, S.
    et al.
    Alegre, D.
    Kreter, A.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Esser, H. G.
    Samm, U.
    Thermo-chemical fuel removal from porous materials by oxygen and nitrogen dioxide2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014065-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermo-chemical removal (TCR), or baking in reactive gases, is a candidate method to control the co-deposit related tritium inventory in fusion devices. TCR can be understood as reaction-diffusion processes in a porous material. O-2-TCR was applied to 150-550 nm thick a-C:D layers with similar textures. A linear relation between the integral TCR rate and the layer thickness, as predicted by the understanding, was observed in the experiment, i.e. the time to remove the hydrogen inventory is independent of its initial amount. TCR with nitrogen dioxide (NO2) at temperatures of 200-350 degrees C was conducted with a set of a-C:D and W-C-H layers. At 350 degrees C NO2 removed similar to 15% porosity a-C:D within 3 min. The O retention in remaining a-C:D was approximate to 10(17) Ocm(-2). An activation energy of approximate to 0.78 eV for reactions of NO2 with D and C was determined. The results were applied for predictions of the TCR effectivity in ITER. The treatment of W-C-H led to O uptake (O/W approximate to 2-3), while W and C contents remained unchanged.

  • 91. Ou, Yiyu
    et al.
    Jokubavicius, Valdas
    Linnarsson, Margareta
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Yakimova, Rositza
    Syväjärvi, Mikael
    Ou, Haiyan
    Characterization of donor-acceptor-pair emission in fluorescent 6H-SiC2012Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T148, s. 014003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigated donor-acceptor-pair emission in N-B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 10(18) cm(-3) is favorable for observing luminescence, and increasing nitrogen results in stronger luminescence. A dopant concentration difference greater than 4x10(18) cm(-3) is proposed to help achieve intense PL. Angular-dependent PL was observed that was attributed to the Fabry-Perot microcavity interference effect, and a strong luminescence intensity in a large emission angle range was also achieved. The results indicate that N-B-doped fluorescent SiC is a good wavelength converter in white LED applications.

  • 92. Panek, R.
    et al.
    Krlin, L.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tskhakaya, D.
    Kuhn, S.
    Svoboda, V.
    Klima, R.
    Pavlo, P.
    Stockel, J.
    Petrzilka, V.
    Anomalous ion diffusion and radial-electric-field generation in a turbulent edge plasma potential weakly correlated in time and space2005Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, nr 4, s. 327-332Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using a simple model of tokamak-edge-plasma turbulence in the form of a spatially periodic and time-independent electrostatic potential, we have found recently a new type of anomalous impurity diffusion in this regime [1], [2]. In the present contribution, we estimate this diffusion in the test-particle approach for a real turbulent potential obtained in an experiment. A significant difference in the impurity dynannics between the Hamiltonian and drift approaches is observed. As an interesting consequence of these dynamics, the possibility of radial-electric-field generation in the turbulence regimes appears. This effect can be of importance in scenarios related to transport barriers.

  • 93. Pardanaud, C.
    et al.
    Rusu, M. I.
    Giacometti, G.
    Martin, C.
    Addab, Y.
    Roubin, P.
    Lungu, C. P.
    Porosnicu, C.
    Jepu, I.
    Dinca, P.
    Lungu, M.
    Pompilian, O. G.
    Mateus, R.
    Alves, E.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Raman microscopy investigation of beryllium materials2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014027Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report for the first time on the ability of Raman microscopy to give information on the structure and composition of Be related samples mimicking plasma facing materials that will be found in ITER. For that purpose, we investigate two types of material. First: Be, W, Be1W9, and Be5W5 deposits containing a few percents of D or N, and second: a Mo mirror exposed to plasma in the main JET chamber (in the framework of the first mirror test in JET with ITER-like wall). We performed atomic quantifications using ion beam analysis for the first samples. We also did atomic force microscopy. We found defect induced Raman bands in Be, Be1W9, and Be5W5 deposits. Molybdenum oxide has been identified showing an enhancement due to a resonance effect in the UV domain.

  • 94. Paul, H.
    et al.
    Greenberger, D. M.
    Stenholm, Stig Torsten
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Schleich, W. P.
    The Stefan-Boltzmann law: two classical laws give a quantum one2015Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T165, artikkel-id 014027Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Due to the universality of blackbody radiation the constant in the Stefan-Boltzmann law connecting the energy density and temperature of blackbody radiation is either a universal constant, or built out of several universal constants. Since the Stefan-Boltzmann law follows from thermodynamics and classical electrodynamics this constant must involve the speed of light and the Boltzmann constant. However, a dimensional analysis points to the existence of an additional universal constant not present in the two classical theories giving birth to the Stefan-Boltzmann law. In the most elementary version this constant has the dimension of an action and is thereby proportional to Planck's constant. We point out this unusual phenomenon of the combination of two classical laws creating a quantum law and speculate about its deeper origin.

  • 95.
    Persson, Stefan
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Wu, Dongping
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Lindgren, Ann Chatrin
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Hellström, Per-Erik
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Zhang, Shi-Li
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Variation of contact resistivity with Ge in TiW/p(+) SiGe contacts2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, s. 49-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dependence of contact resistivity on the Ge content in Si1-xGex is examined for TiW/p(+) Si1-xGex interfaces. Measurements are made on contacts with epitaxial Si1-xGex layers either at the surface or buried under a Si cap layer of various thicknesses. The contact resistivity is found to decrease by an order of magnitude with increasing Ge content from 0 to 30 at. %, which is attributed to an increase in the valence band energy of p(+) Si1-xGex. The measured contact resistivity is compared with a theoretical model, and the experimental results agree well with the modelled ones.

  • 96.
    Petersson, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Brezinsek, S.
    Kreter, A.
    Möller, S.
    Hakola, A.
    Mayer, M.
    Miettunen, J.
    Airila, M. I.
    Makkonen, T.
    Neu, R.
    Rohde, V.
    Overview of nitrogen-15 application as a tracer gas for material migration and retention studies in tokamaks2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014042-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental and analytical procedures related to the application of nitrogen-15 isotope for material migration studies have been developed and used for tracer experiments in the TEXTOR and ASDEX-Upgrade tokamaks in order to assess the retention of nitrogen in plasma-facing components made of graphite and tungsten. The surface study was performed by time-of-flight heavy ion elastic recoil detection analysis and by means of nuclear reaction analysis based on the N-15(p, gamma alpha)C-12 process. In both tokamaks nitrogen retention has exceeded 10% of the injected gas. In ASDEX-Upgrade the largest fraction of N-15 has been detected on protruding parts near the injection port, while around 4% has been found in the divertor. The ASDEX-Upgrade results have also been modeled. Helium trapping has been measured in deposits containing tungsten and nitrogen.

  • 97.
    Petersson, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Pegourie, B.
    Micro-distribution of fuel and metal in carbon-based plasma-facing materials2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surfaces of carbon fibre composite tiles from the toriodal pump limiter of Tore Supra were examined with ion beams to determine simultaneously the distribution of co-deposited deuterium and metallic plasma impurities (i. e. steel components). With a (3)He(+) ion beam the reaction (2)D((3)He, p)(4)He was used for deuterium, (12)C((3)He, p)(14)N for carbon, whereas beam-induced x-ray emission and back-scattered ions served for the detection of heavier elements. Measurements were made both with a 1mm beam and by a micro-beam focused down to 20 mu m spot size and scanned over the sample to obtain maps of the different elements. Distribution maps of different elements-fuel and metal species-are presented for four distinct regions on the limiter: erosion zone, shadowed area, thin deposits and thick flaking deposits.

  • 98. Plimak, L. , I
    et al.
    Stenholm, Stig
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Ulm, Inst Quantenphys, D-89069 Ulm, Germany.;KTH, Royal Inst Technol, Phys Dept, Stockholm, Sweden.;HUT, Lab Computat Engn, Espoo, Finland..
    Quantum chains and regularisation of quantum dynamics2018Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 93, nr 10, artikkel-id 104002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We argue that the origin of ultraviolet divergences in quantum field theory (QFT) may be not in the perturbative expansion, but in the fact that, mathematically, the Heisenberg equations of motion are not properly defined. Divergences similar to those in QFT are shown to exist in seemingly simple quantum problems with parametric Hamiltonians. These divergences may be suppressed by formally replacing the system in question by a quantum chain. The latter is a dynamically regularised system specified by two postulates, imposing conditions on its response properties. The kinematical postulate specifies the linear response, the dynamical postulate extends it to nonlinear dynamics. The kinematical postulate uniquely determines the mathematical environment (quantisation with indefinite metric), hence the term. Using the Klein-Gordon, Gupta-Bleuler and Dirac fields as examples we show that the concept of quantum chain generalises seamlessly to relativistic quantum fields. Perspectives of using quantum chains as regularisation devices in QFT are discussed.

  • 99. Plimak, L. I.
    et al.
    Stenholm, Stig Torsten
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Schleich, W. P.
    Operator ordering and causality2012Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T147, s. 014026-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A formal implementation of the concepts of mesoscopic electromagnetic interaction and of the propagating wave in quantum electrodynamics beyond the rotating wave approximation is discussed. Used as a guide, these concepts lead to a natural resolution of a long-standing controversy: causality violations in the Glauber-Kelley-Kleiner photodetection theory. The Glauber-Kelley-Kleiner definition of the time-normal operator ordering must be amended without the rotating wave approximation, which eliminates all causality problems.

  • 100.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    N = Z nuclei: a laboratory for neutron-proton collective mode2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, nr 1, artikkel-id 013009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The neutron-neutron and proton-proton pairing correlations have long been recognized to be the dominant many-body correlation beyond the nuclear mean field since the introduction of pairing mechanism by Bohr, Mottelson and Pines nearly 60 years ago. Nevertheless, few conclusions have been reached concerning the existence of analogous neutron-proton (np) pair correlated state. One can see a renaissance in np correlation studies in relation to the significant progress in radioactive ion beam facilities and detection techniques. The np pairs can couple isospin T = 1 (isovector) or 0 (isoscalar). In the isovector channel, the angular momentum zero component is expected to be the most important one. On the other hand, as one may infer from the general properties of the np two-body interaction, in the isoscalar channel, both the np pairs with minimum (J = 1) and maximum (J = 2j) spin values can be important. In this contribution, we will discuss the possible evidence for np pair coupling from a different perspective and analyze its influence on interesting phenomena including the Wigner effect and mass correlations in odd-odd nuclei. In particular, we will explain the spin-aligned pair coupling scheme and quartet coupling involving pairs with maximum (J = 2j) spin values.

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