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  • 101.
    Raadu, Michael A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Generalised Sagdeev potentials for dusty plasmas with varying grain charges2003Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 68, nr 4, s. 266-270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Grain charges in a dusty plasma are deter-mined by the random currents from the ambient plasma and vary with the local conditions. The charge on a slowly moving grain will be close to the locally determined equilibrium. given for zero net current to the grain. For a steady electrostatic structure (e.g., solitary wave, double layer) integrals of motion for grains with varying charge can then be found. (These integrals reduce to the total energy if the charge is constant. but in general the electrostatic term becomes an integral of the grain charge with respect to the potential.) Steady state solutions of Vlasov's equation are piecewise given by arbitrary functions of these integrals of motion. A generalised Sagdeev (Classical) potential can be found, which is. to within an added constant. equal to minus the sum of the total particle pressures (including that of the grains). This extends the well known equivalence found for conventional plasmas and dusty plasmas with constant grain charges. The analysis of dust acoustic solitary waves is modified by additional terms proportional to potential derivatives of the charge. A grain size distribution may be incorporated. The second derivative of the Sagdeev potential (leading to the generalised Bohm condition) is then Riven in terms of the same effective distribution function as found for linear electrostatic modes. Comparisons are made with several analyses of nonlinear electrostatic structures including dynamical charging.

  • 102. Radamson, H. H.
    et al.
    Bentzen, A.
    Menon, C.
    Landgren, Gunnar.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Observed critical thickness in selectively and non-selectively grown Si1-xGex layers on patterned substrates2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 42-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Relaxation of SiGe layers grown selectively or non-selectively on oxide-patterned substrates using reduced pressure chemical vapor deposition was investigated. The influences of the buffer layer, the polycrystalline layer on the oxide and the opening size on the critical thickness for relaxation of SiGe layers have been studied in detail. High resolution reciprocal lattice mapping, atomic force microscopy and Normanski optical microscope have been used as the main characterization tools.

  • 103. Radamson, H. H.
    et al.
    Mohadjeri, B.
    Menon, C.
    Bentzen, A.
    Grahn, J.
    Landgren, Gunnar.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Growth of high frequency SiGe heterojunction bipolar transistors structures2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 45-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth of heterojuntion bipolar transistor structures using chemical vapor deposition has been investigated. Generation of defects in selectively or nonselectively grown collector layers using arsenic as the dopant has been studied. Minimizing the defect density in SiGe base layers by optimizing the growth rate has also been investigated in detail. High resolution reciprocal lattice mapping, atomic force microscopy and secondary ion mass spectrometry have been used as the main characterization tools.

  • 104.
    Radamson, Henry
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Hållstedt, Julius
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Isheden, Christian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Östling, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Formation of shallow source/drain junctions in MOSFET structures by using Cl-based processes in reduced pressure CVD reactors2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, s. 97-100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel process to form shallow junctions for source) drain application in CMOS structures is presented. The method consists of two steps; first an HCl-etch followed by SiCl2H2-based selective epitaxy in the same run in a reduced pressure chemical vapour deposition chamber. Optimization of etch and epitaxy processes have been investigated and the active dopant concentration in SiGe layers grown was measured directly in the device openings.

  • 105.
    Rubel, Marek
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Coad, J. P.
    CCFE/EURATOM Fusion Association, Culham Science Centre.
    Temmerman, G. De
    FOM Institute for Plasma Physics.
    Likonen, J.
    Association EURATOM–TEKES, VTT, Espoo.
    Marot, L.
    Department of Physics, University of Basel.
    Schmidt, A.
    Institute for Energy and Climate Research, Forschungszentrum Jülich,.
    Widdowson, A.
    CCFE/EURATOM Fusion Association, Culham Science Centre.
    Overview of the second stage in the comprehensive mirrors test in JET2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014070-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first mirror test for ITER in JET with carbon walls has been completed. Thirty polycrystalline Mo mirrors including four coated with a 1 μm rhodium (Rh) film were exposed to plasma in the divertor region and in the main chamber. The mirrors were installed in eight cassettes of pan-pipe shape. The reflectivity of all mirrors exposed in the divertor has been degraded by 80–90% because of the formation of thick (>20 μm) flaking co-deposits on surfaces. Only small reflectivity losses (5–10%) occurred on mirrors located at the channel mouth of the cassettes from the main chamber wall. This is due to the in situremoval of deposited species by charge exchange neutrals. Deuterium, 12C and 9Be are the main isotopes detected on surfaces, but other isotopes (13C) are also found in some locations, thus indicating differences in the material migration. Rhodium coatings with an initial reflectivity that is 30% better than that of pure Mo survived the test without detachment, but their resultant reflectivity was the same as that of the exposed Mo surfaces.

  • 106.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Analysis of plasma facing materials: material migration and fuel retention2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T123, s. 54-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Key issues in the characterization and analysis of plasma facing materials are presented. The influence of plasma operation on the material modification and fuel inventory is emphasized. The role of analysis in the process of material selection and qualification for usage in controlled fusion devices is also addressed. Various methods for the determination of fuel species in wall components are reviewed. The underlying physics of methods, practical aspects of analysis procedures and special instrumentation for studies of plasma facing components are described.

  • 107.
    Rubel, Marek J.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Coad, J. P.
    Wienhold, P.
    Matthews, G.
    Philipps, V.
    Stamp, M.
    Tanabe, T.
    Fuel inventory and co-deposition in grooves and gaps of divertor and limiter structures2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T111, s. 112-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasma facing components from JET and TEXTOR were studied. The emphasis was on the comparison of co-deposition, material mixing and fuel inventory on plasma facing and side surfaces of tiles, i.e. in gaps separating the tiles. Integrated fuel content in gaps of the Mk-I JET divertor floor was approximately two times greater than detected on the plasma facing surfaces. Taking into account similarities between the Mk-I structure and the castellation in the ITER divertor, the impact of the tile shaping on the tritium inventory is addressed. Deposition on the side of limiter tiles in TEXTOR was around 3-5% of that on the plasma facing surfaces. Experiments aiming at a deeper insight into the deposition on ITER-relevant components are also proposed.

  • 108.
    Rubel, Marek J.
    et al.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Philipps, V.
    Tanabe, T.
    Wienhold, P.
    Freisinger, M.
    Linke, J.
    von Seggern, J.
    Wessel, E.
    Thick co-deposits and dust in controlled fusion devices with carbon walls: Fuel inventory and growth rate of co-deposited layers2003Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T103, s. 20-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent results regarding the formation of co-deposits, fuel accumulation and overall material transport at the TEXTOR tokamak are described. Two categories of brittle flaking co-deposits were identified: (i) smooth stratified layers of a thickness of up to 50 mum and a fuel content of up to 16 at.%. (ii) granular and columnar structures reaching 1 mm in thickness and containing around 0.5 at.% of fuel species. They were formed on the blades of the toroidal belt pump limiter (similar to 15000 s of plasma operation) and on the neutraliser plates of this limiter (similar to 90000 s), respectively. A comparison is made to the fuel inventory measured in other controlled fusion devices with carbon walls.

  • 109.
    Rubel, Marek
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Moon, Soonwoo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik.
    Krawczynska, A.
    Fortuna-Zalesna, E.
    Gilbert, M.
    Plocinski, T.
    Widdowson, A.
    Metallic mirrors for plasma diagnosis in current and future reactors: tests for ITER and DEMO2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014061Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Optical spectroscopy and imaging diagnostics in next-step fusion devices will rely on metallic mirrors. The performance of mirrors is studied in present-day tokamaks and in laboratory systems. This work deals with comprehensive tests of mirrors: (a) exposed in JET with the ITER-like wall (JET-ILW); (b) irradiated by hydrogen, helium and heavy ions to simulate transmutation effects and damage which may be induced by neutrons under reactor conditions. The emphasis has been on surface modification: deposited layers on JET mirrors from the divertor and on near-surface damage in ion-irradiated targets. Analyses performed with ion beams, microscopy and spectro-photometry techniques have revealed: (i) the formation of multiple co-deposited layers; (ii) flaking-off of the layers already in the tokamak, despite the small thickness (130-200 nm) of the granular deposits; (iii) deposition of dust particles (0.2-5 mu m, 300-400 mm(-2)) composed mainly of tungsten and nickel; (iv) that the stepwise irradiation of up to 30 dpa by heavy ions (Mo, Zr or Nb) caused only small changes in the optical performance, in some cases even improving reflectivity due to the removal of the surface oxide layer; (v) significant reflectivity degradation related to bubble formation caused by the irradiation with He and H ions.

  • 110. Ruset, C.
    et al.
    Grigore, E.
    Luculescu, C.
    Tiseanu, I.
    Likonen, J.
    Mayer, M.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Matthews, G. F.
    Investigation on the erosion/deposition processes in the ITER-like wall divertor at JET using glow discharge optical emission spectrometry technique2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014049Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As a complementary method to Rutherford back scattering (RBS), glow discharge optical emission spectrometry (GDOES) was used to investigate the depth profiles of W, Mo, Be, O and C concentrations into marker coatings (CFC/Mo/W/Mo/W) and the substrate of divertor tiles up to a depth of about 100 μm. A number of 10 samples cored from particular areas of the divertor tiles were analyzed. The results presented in this paper are valid only for those areas and they cannot be extrapolated to the entire tile. Significant deposition of Be was measured on Tile 3 (near to the top), Tile 6 (at about 40 mm from the innermost edge) and especially on Tile 0 (HFGC). Preliminary experiments seem to indicate a penetration of Be through the pores and imperfections of CFC material up to a depth of 100 μm in some cases. No erosion and a thin layer of Be (<1 μm) was detected on Tiles 4, 7 and 8. On Tile 1 no erosion was found at about 1/3 from bottom.

  • 111. Rypdal, K.
    et al.
    Ratynskaia, Svetlana V.
    Plasma profiles, waves and anomalous transport in a purely toroidal plasma modified by a biased internal anode2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T122, s. 52-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two-dimensional (2D) plasma profiles, gradient-driven low frequency electrostatic waves and anomalous particle transport are studied experimentally in a purely toroidal plasma configuration. The plasma is produced by a negatively biased, emissive cathode in conjunction with a variably biased anode plate localized on the same field line. Nearly circularly symmetric potential profiles, positive or negative, can be obtained by varying the anode plate bias. Confinement loss in the form of plasma ejection in the major radius direction is only observed when the anode is biased close to ground potential. For the cases of circularly symmetric plasma flow electrostatic flute modes with poloidal mode number m = 1 and m = 2 are identified as unstable on the low- field side of the density maximum, but indications are also given that they coexist with spatially quasi-uniform oscillations and, for low frequencies, with an ion acoustic mode with toroidal mode number n = 1 propagating parallel to the magnetic field. The anomalous particle flux density is found to be non- uniformly distributed on a toroidal surface, and the main flux is passed through two lobes directed almost vertically upwards and downwards, while almost no flux takes place along the major radius direction.

  • 112.
    Scheffel, Jan
    KTH.
    Linear MHD Equilibria in Toroidal Geometry - Exact and Approximate Solution1984Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 30, s. 216-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear Grad-Shafranov equation for a toroidal, axisymmetric plasma is solved analytically. Exact solutions are given in terms of confluent hyper-geometric functions. As an alternative, simple and accurate WKBJ solutions are presented. With parabolic pressure profiles, both hollow and peaked toroidal current density profiles are obtained. As an example the equilibrium of a z-pinch with a square-shaped cross section is derived.

  • 113. Sergienko, G.
    et al.
    Bazylev, B.
    Hirai, T.
    Huber, A.
    Kreter, A.
    Mertens, Ph
    Nedospasov, A.
    Philipps, V.
    Pospieszczyk, A.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Samm, U.
    Schweer, B.
    Sundelin, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Tokar, M.
    Wessel, E.
    Textor team,
    Experience with bulk tungsten test-limiters under high heat loads: melting and melt layer propagation2007Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T128, s. 81-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper provides an overview of processes and underlying physics governing tungsten melt erosion in the fusion plasma environment. Experiments with three different bulk tungsten test-limiters were performed in TEXTOR: (i) thermally insulated solid plate fixed on a graphite roof-like limiter heated up by the plasma to the melting point, (ii) macro-brush of the ITER-relevant castellated structure and (iii) lamellae structure developed for the JET divertor. The main objectives were to determine the metal surface damage, the formation of the melt layer and its motion in the magnetic field. PHEMOBRID-3D and MEMOS-1.5D numerical codes were used to simulate the experiment with the roof-like test-limiter. Both experiments and simulation showed that the melting of tungsten can lead to a large material redistribution due to thermo-electron emission currents without ejection of molten material to the plasma.

  • 114.
    Shen, Jian Qi
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Automatic generation of nonadiabatic conditional geometric phase shift with a noncoplanar fibre system2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 73, nr 1, s. 79-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new scheme for realizing a nonadiabatic conditional geometric phase shift via a noncoplanar (coiled) fibre system is presented. It is shown that the effective Hamiltonian that describes the interaction of polarized photons with a fibre medium is just the Wang-Matsumoto type of Hamiltonian. This, therefore, means that the coiled fibre system may be an ideal implementation for realizing the nonadiabatic geometric phase gates involved in the topological quantum computation. A remarkable feature of the present method is that it can automatically meet the conditions and requirements proposed in the Wang-Matsumoto nuclear magnetic resonance (NMR) scheme: specifically, (i) in the coiled fibre system, the dynamical phase of photon wavefunction caused by the interaction Hamiltonian automatically vanishes; (ii) the Wang-Matsumoto requirement for the parameters in the Wang-Matsumoto NMR Hamiltonian can be exactly satisfied automatically in such a fibre system; and (iii) the conditional initial state can be easily achieved by manipulating the initial wave vector of polarized photons.

  • 115.
    Shen, Jianqi
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Cheng, Yao
    Simulating the vector potential of gravitomagnetic monopole using spiral motions of confined spinning particles2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 78, nr 4, s. 045004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exact solutions to the time-dependent Schrodinger equation that governs the spiral motions of spinning particles are obtained, and the geometric phases that can be written as path integral of the vector potential of gravitomagnetic monopole (dual mass) are studied. Two illustrative examples of the confined spinning particles (e. g. a photon moving in a helical fiber and an electron confined by a planar radial electric field) are considered. It is shown that the confined spinning particles undergoing spiral motions seem to move inside a gravitomagnetic field produced by an equivalent gravitomagnetic monopole, i.e. the wavefunctions in the spiral motions of confined spinning particles acquire geometric phases, which are equivalent to the phase shift of a zero-spin particle that moves in the vector potential of a gravitomagnetic monopole. This means that the spiral motions of the confined spinning particles in proper potential fields can be used to simulate the gravitomagnetic vector potentials of dual mass. Though there is at present no evidence for the existence of gravitomagnetic monopole, the work presented here may stimulate interest in some areas such as the gravitationally induced quantum effects (relativistic quantum gravitational effects).

  • 116.
    Snellman, Jan Eskil
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Rheinhardt, Matthias
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Käpylä, Petri J.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Mantere, Marit J.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Mean-field closure parameters for passive scalar turbulence2012Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 86, nr 1, s. 018406-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Direct numerical simulations (DNSs) of isotropically forced homogeneous stationary turbulence with an imposed passive scalar concentration gradient are compared with an analytical closure model which provides evolution equations for the mean passive scalar flux and variance. Triple correlations of fluctuations appearing in these equations are described in terms of relaxation terms proportional to the quadratic correlations. Three methods are used to extract the relaxation timescales tau(i) from DNSs. Firstly, we insert the closure ansatz into our equations, assume stationarity and solve for tau(i). Secondly, we use only the closure ansatz itself and obtain tau(i) from the ratio of quadratic and triple correlations. Thirdly, we remove the imposed passive scalar gradient and fit an exponential law to the decaying solution. We vary the Reynolds (Re) and Peclet numbers (while fixing their ratio at unity) and the degree of scale separation and find for large Re a fair correspondence between the different methods. The ratio of the turbulent relaxation time of the passive scalar flux to the turnover time of the turbulent eddies is of the order of 3, which is in remarkable agreement with earlier work. Finally, we make an effort to extract the relaxation timescales relevant for the viscous and diffusive effects. We find two regimes that are valid for small and large Re, respectively, but the dependence of the parameters on scale separation suggests that they are not universal.

  • 117. Somesfalean, G.
    et al.
    Alnis, J.
    Svanberg, S.
    Derkatch, A.
    Mannervik, S.
    Rostohar, D.
    Royen, P.
    Schef, P.
    Norlin, Lars-Olov
    KTH, Tidigare Institutioner, Fysik.
    Violet diode laser in time-resolved stored-ion spectroscopy2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 69, nr 2, s. 98-103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lifetime measurements of the metastable 3d D-2(3/2) level in singly charged calcium were performed using the newly developed violet diode laser operated in an external cavity arrangement. The laser was employed on stored ions at the CRYRING facility to optically pump the resonance line at 397 nm. In combination with laser probing at 866 nm this detection scheme gave the possibility to record the lifetime of this level. which has a radiative lifetime of about 1 s.

  • 118. Stancalie, V.
    et al.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    Study of opacity effects on emission lines at EXTRAP T2R RFP2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 66, nr 6, s. 444-448Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the influence of opacity on hydrogen (H-alpha and Ly-beta) and Li-like oxygen emission lines from the EXTRAP T2R reversed field pinch. We used the Atomic Data Analysis System (AzDAS) based on the escape factor approximation for radiative transfer to calculate metastable and excited population densities via a collisional-radiative model. Population escape factor. emergent escape factor and modified line profiles are plotted vs. optical depth. The simulated emission line ratios in the density/temperature plane are in good agreement with experimental data for electron density and temperature measurements.

  • 119. Suvar, E.
    et al.
    Haralson, E.
    Forsberg, M.
    Radamson, H.
    Wang, Yong-Bin
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Grahn, J. V.
    A base-collector architecture for SiGeHBTs using low-temperature CVD epitaxy combined with chemical-mechanical polishing2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 64-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new collector technology intended for an integrated high-speed SiGe heterojunction bipolar transistor (HBT) is reported. The collector was fabricated by selective epitaxial growth (SEG) using chemical vapor deposition at 770degreesC under reduced pressure (20 torr) using SiH2Cl2 as silicon precursor and PH3 as n-type dopant source. Chemical-mechanical polishing (CMP) was applied to the overgrown SEG collector in order to achieve a smooth surface in level with the surrounding oxide. Finally, a SiGe base doped with boron was deposited using non-selective epitaxial growth (NSEG) at 650degreesC. The topography of the collector is inspected after each process step by atomic force microscopy and the topography of the completed collector/base stack indicates that this structure is promising for fabrication of the emitter window. A further advantage with the CMP procedure is the elimination of phosphorous segregation as evidenced by secondary ion mass spectroscopy of the base-collector stack.

  • 120.
    Suvar, Erdal
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Haralson, Erik
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Hållstedt, Julius
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Radamson, Henry H.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Östling, Mikael
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    As- or P-doped Si layers grown by RPCVD for emitter application in SiGeCHBTs2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, s. 34-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new module for the emitter formation in a bipolar transistor is presented. Arsenic- or phosphorus-doped polycrystalline silicon layer for the emitter formation is deposited in a reduced pressure chemical vapor deposition reactor using silane as the silicon source gas. Characteristics such as the carrier concentration, conductivity, surface morphology, and thermal stability of the polycrystalline-silicon layer as well as the influence this layer has on a SiGeC transistor structure during the drive-in step area studied. The active carrier concentration of the as-grown sample is strongly dependent on the deposition temperature, especially arsenic doped layers which exhibit more than one order of magnitude difference. However, the carrier concentration for the As- or P-doped layer were comparable to that of a standard in-situ doped poly-crystalline layer after a dopant activation at 925 degrees C for 10s.

  • 121. Syväjärvi, M.
    et al.
    Mueller, J.
    Sun, J. W.
    Grivickas, V.
    Ou, Y.
    Jokubavicius, V.
    Hens, P.
    Kaisr, M.
    Ariyawong, K.
    Gulbinas, K.
    Liljedahl, R.
    Linnarsson, Margareta K.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Kamiyama, S.
    Wellmann, P.
    Spiecker, E.
    Ou, H.
    Fluorescent SiC as a new material for white LEDs2012Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T148, s. 014002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current III-V-based white light-emitting diodes (LEDs) are available. However, their yellow phosphor converter is not efficient at high currents and includes rare-earth metals, which are becoming scarce. In this paper, we present the growth of a fluorescent silicon carbide material that is obtained by nitrogen and boron doping and that acts as a converter using a semiconductor. The luminescence is obtained at room temperature, and shows a broad luminescence band characteristic of donor-to-acceptor pair recombination. Photoluminescence intensities and carrier lifetimes reflect a sensitivity to nitrogen and boron concentrations. For an LED device, the growth needs to apply low-off-axis substrates. We show by ultra-high-resolution analytical transmission electron microscopy using aberration-corrected electrons that the growth mechanism can be stable and that there is a perfect epitaxial relation from the low-off-axis substrate and the doped layer even when there is step-bunching.

  • 122.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Major achievements and challenges of fusion research2015Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, nr 9, artikkel-id 098002Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The ITER project is truly at the frontier of knowledge, a collective effort to explore the tantalizing future of free, clean and inexhaustible energy offered by nuclear fusion. Where the Large Hadron Collider at CERN pushes the boundaries of physics to find the origins of matter, the ITER Project seeks to give humans an endless stream of power which could have potentially game-changing consequences for the entire planet. Seminal contributions to the general physics knowledge accomplished by the plasma physics research for the benefit of the ITER project will be brought to light. The legacy of Professor H Alfven within the framework of the ITER project will be described.

  • 123.
    Tendler, Michael
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Selforganisation in plasma physics: Special Issue Dedicated to Professor Lennart Stenflo on the Occasion of His 65th Birthday2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, ISSN 0281-1847, Vol. T113, s. 51-55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The bottom line of modern plasma physics addressing a many body problem is the lack of thermodynamic potentials for the system in which fluxes are no longer linear functions of forces or gradients. Indeed far from the classical equilibrium, a system can still converge to a stationary state, yet not defined by the proper thermodynamic potential in contrast to the entropy production principle valid only for a linear or weakly nonlinear system. In this case, we confront an important issue of stability of a strongly nonequilibrium system occurring and lacking the thermodynamic potential. In a linear system the equilibrium is defined by the minimum of the potential and therefore the stability of the resulting steady - state is easily found. Of course, any fluctuation causes a deviation from the equilibrium. Yet, linear or weakly nonlinear system will return to this steady state due to the second law of thermodynamics. Hence, the existence of the thermodynamic potential makes the equilibrium very robust. Given the potential, any evolution of a weakly nonlinear system will result in a static stationary state. In contrast, a strongly nonlinear system may loose a steady state very easily due to instability perturbed by fluctuations. If this is the case the fluctuation will be amplified until a very different steady state not described by a minimum of the thermodynamic potential emerges. In more detail, instability in a strongly nonlinear situation has always to exceed a given threshold in order to yield a different equilibrium far from an original static steady state. In fluids and plasmas it is well-known that any laminar motion can transform into a turbulent motion once a given fluid velocity is exceeded. It may appear that this transition yields a chaotic strongly fluctuating equilibrium. Indeed although at the macroscopic level this novel equilibrium may appear to be a complete disorder and chaos, it is found experimentally that at the microscopic level the new equilibrium is characterised by a highly ordered vortices [1] resulting due to the inherent selforganization of this system. Here, it is important to keep in mind that fluid equations describing this phenomenon are highly nonlinear. Multiple scales emerge both in space and in time, thereby pointing to the scale free nature of the fractal geometry. The convection emerging due to multiscale vortices is organised to enhance the thermal conductivity in contrast to the second law of thermodynamics. The reason for this is that a fluctuation bound to dissipate within the framework of the weakly nonlinear approach is significantly amplified and ultimately governs the system. The entropy is of course provided by an external source in the environment and there is no contradiction to the second law. Hence, a novel highly organised equilibrium emerges which may also be time dependent. To this end, turbulent vortices differ very much from equilibrium structures like crystals because here thermal fluxes provide the order in contrast to the dissipation only in linear systems. Novel dissipative structures arise from a chaotic particle motion on all possible time and space scales.

  • 124.
    Tesinsky, Milan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Reaktorfysik.
    Andersson, Pernilla
    Gustavsson, Cecilia
    Pomp, Stephan
    Österlund, Michael
    Blomgren, Jan
    Bevilacqua, Riccardo
    Hjalmarsson, Anders
    Kolozhvari, Anatoly
    LeColley, Francois-René
    Marie, Nathalie
    Prokofiev, Alexander V.
    Simutkin, Vasily
    Tippawan, Udomrat
    MCNPX simulations of the SCANDAL setup for measurement of neutron scattering cross section at 175MeV2010Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 81, nr 6, s. 065202-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Scattered Nucleon Detection Assembly (SCANDAL) setup at The Svedberg Laboratory has been used to produce neutron elastic scattering cross section data at 175MeV for bismuth and iron. This work presents MCNPX simulations of the experimental setup and aims to describe processes and data important for the upcoming off-line data analysis. In the experiment, neutrons scattered off the target are converted to protons, which are stopped in scintillator crystals. The results include a description of the proton spectra dependence on the neutron-to-proton conversion angle, suggesting a cut at a conversion angle of 15.2 degrees. Calculation of the hit position gates indicates high proton leakage from the crystals. A study of the converter describes the role of its chemical composition and also the role of other plastic scintillators on the proton spectra. The neutron-to-proton conversion efficiency of the converter simulated by MCNPX is 5.1x10(-4) and corresponds to theoretical predictions.

  • 125.
    Thorén, Emil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bazylev, B.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Krieger, K.
    Pitts, R. A.
    Pestchanyi, S.
    Komm, M.
    Sieglin, B.
    Simulations with current constraints of ELM-induced tungsten melt motion in ASDEX Upgrade2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 126.
    Thylwe, Karl-Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Amplitude-phase formula for the S-matrix derived from invariants of the reduced first-order radial Dirac equation2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 78, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A formula for calculating the Dirac S-matrix for central Lorentz scalar and vector potentials is derived by use of a new amplitude-phase method. The derivation also makes use of certain invariants of the reduced 2-spinor radial Dirac equations.

  • 127.
    Thylwe, Karl-Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Amplitude-phase methods for analyzing the radial Dirac equation: calculation of scattering phase shifts2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Approaches inspired by a recent amplitude-phase method for analyzing the radial Dirac equation are presented to calculate phase shifts. Regarding the spin- and pseudo-spin symmetries of relativistic spectra, the coupled first-order and the decoupled second-order differential forms of the radial Dirac equation are investigated by using a novel and the 'classical' amplitude-phase methods, respectively. The quasi non-relativistic limit c --> +infinity of the amplitude- phase formulae is discussed for both positive and negative energies. In the positive (E > mc(2)) low-energy region, the relativistic effects of scattering phase shifts are discussed based on two scattering potential models. Results are compared with those of non-relativistic calculations. In particular, the numerical results obtained from a rational approximation of the Thomas-Fermi potential are discussed in some detail.

  • 128.
    Thylwe, Karl-Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Dirac resonance energies for central potentials with different Lorentz-type potential couplings2010Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 81, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The amplitude-phase method is applied to relativistic Dirac-particle resonances related to electron-atom collisions. Complex-energy resonance poles of the S matrix in central potentials of differing Lorentz couplings are studied near the non-relativistic limit. It is confirmed that an equal mixture of a Lorentz vector-type potential (with a single time component) and a Lorentz scalar-type potential of the same radial shape makes the interaction essentially spin independent, as if spin does not couple to orbital angular momentum. Hence, resonance poles of the S matrix depend simply on the orbital angular momentum and the radial quantum number in a similar way as in the Schrodinger limit and in the Klein-Gordon equation. In a Lorentz-vector potential model, there is a splitting of pole positions, but the splitting may be surprisingly small, as demonstrated for one of the potentials considered. The numerical method used automatically assigns a vibrational (radial) quantum number to the resonance state, which is usually a characteristic feature of semiclassical methods.

  • 129.
    Thylwe, Karl-Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Discontinuous radial potentials, bound states and Dirac equations2019Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 94, nr 6, artikkel-id 065201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Discontinuous, radial 'square-well' potentials of scalar and (time-component) vector types require special quantization conditions in Dirac equations transformed to second-order differential equations. Quantization conditions for positive energies are derived from first-order and second-order differential equations using amplitude-phase methods. Analytic condition for no orbital angular momentum of the large spinor component is obtained. Numerical applications relevant to independent-nucleon shell models illustrate level shifts due to shape (square-well/Woods-Saxon) differences.

  • 130.
    Thylwe, Karl-Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Relativistic energy shifts of negative-ion bound states: the rational function Thomas-Fermi potential model2012Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 85, nr 6, s. 065009-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rational function Thomas-Fermi (RTF) potential recently used for describing electron-atom scattering interactions is investigated as to its bound (negative-ion) states. Although the (static) RTF potential may account for some relativistic and many-body corrections, this study focuses on (relativistic) dynamical aspects of the 'extra' electron in the negative-ion bound states. Some exotic states near threshold are shown to exist in the Dirac equations but not in the Schrodinger equation that neglects the spin of the 'extra' electron. Results are presented for the two large atomic charge numbers Z = 54 and Z = 64.

  • 131.
    Thylwe, Karl-Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Hamzavi, Majid
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    On pseudospin symmetry of Dirac states2013Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, nr 2, s. 025004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Some aspects of pseudospin symmetry for bound Dirac particle states of finite potentials vanishing as r -> +infinity are discussed. Energy states showing pseudospin symmetry are of interest in nuclear spectroscopy for states explained by a single nucleon interacting with a heavy nucleus. Such states may be approximated by Dirac theory as Dirac particle states with positive relativistic energies and/or Dirac anti-particles with negative relativistic energies. It is confirmed, in this study of an exponential-shaped potential model of vector, scalar and tensor interactions, that positive-energy pseudospin symmetric Dirac states exist in relativistic quantum mechanics, but not in the Schrodinger theory, and that tensor coupling may play an important role in the pseudospin symmetry.

  • 132.
    Thylwe, Karl-Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Linnaeus, Staffan
    Semiclassical aspects and supersymmetry of bound Dirac states for central pseudo-scalar potentials2011Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 84, nr 2, s. 025006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Relativistic bound states for a linear, radial pseudo-scalar potential model are discussed. The two radial Dirac components are known to have a close connection to partner states in super-symmetric quantum mechanical theory. The pseudo-scalar potential plays the role of the 'super potential'. Hence, the Dirac components satisfy decoupled Schrodinger-type equations with isospectral, so-called, 'partner potentials' except possibly for a single state; the ground state corresponding to one of the partner potentials. The energy spectrum of a confining linear radial potential is discussed in some detail. Accurate amplitude-phase computations and a novel semiclassical (phase-integral) approach are presented.

  • 133.
    Thylwe, Karl-Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    McCabe, Patrick
    A theoretical study of spin-angular behaviors of potential scattering resonances2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, nr 8, s. 085401-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Resonance scattering of a Dirac particle (electron) in a screened Coulomb potential (of Lorentz vector type) is investigated. The so-called direct and spin-flip differential cross-sections (DCSs) for Dirac particles are analyzed by a partial-wave analysis, as well as the spin-polarization parameters, here denoted S, T and U. This model study of angular as well as energy behaviors shows that DCSs, at forward and backward angles, together with the polarization parameter. seem to be best indicators of energy and orbital angular momentum of sharp, isolated, resonances.

  • 134. Tsavalas, P.
    et al.
    Lagoyannis, A.
    Mergia, K.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Triantou, K.
    Harissopulos, S.
    Kokkoris, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Be ITER-like wall at the JET tokamak under plasma2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014049Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The JET tokamak is operated with beryllium and tungsten plasma-facing components to prepare for the exploitation of ITER. To determine beryllium erosion and migration in JET a set of markers were installed. Specimens from different beryllium marker tiles of the main wall of the ITER-like wall (ILW) JET tokamak from the first and the second D-D campaign were analyzed with nuclear reaction analysis, x-ray fluorescence spectroscopy, scanning electron microscopy and x-ray diffraction (XRD). Emphasis was on the determination of carbon plasma impurities deposited on beryllium surfaces. The C-12(d, p(0))C-13 reaction was used to quantify carbon deposition and to determine depth profiles. Carbon quantities on the surface of the Be tiles are low, varying from (0.35 +/- 0.07) x 10(17) to (11.8 +/- 0.6) x 10(17) at cm(-2) in the deposition depth from 0.4 to 6.7 mu m, respectively. In the 0.4-0.5 mm wide grooves of castellation sides the carbon content is found up to (14.3 +/- 2.5) x 10(17) at cm(-2) while it is higher (up to (38 +/- 4) x 10(17) at cm(-2)) in wider gaps (0.8 mm) separating tile segments. Oxygen (O), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni) and tungsten (W) were detected in all samples exposed to plasma and the reference one but at lower quantities at the latter. In the central part of the Inner Wall Guard Limiter from the first ILW campaign and in the Outer Poloidal Limiter from the second ILW campaign the Ni interlayer has been completely eroded. XRD shows the formation of BeNi in most specimens.

  • 135.
    Tu, Yaoquan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Costa Felicíssimo, Viviane
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Fernandes Guimarães, Freddy
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Gel’mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Mechanical action of infrared light on atoms and molecules through a rectification of the electric force2009Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 80, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the mechanical action of infrared light on atoms and molecules based on the rectification of the electric force. This mechanism is qualitatively different from the conventional ways of controlling photochemistry. The rectification of the electric force originates from the synchronous charge transfer induced by the laser field. This brings about an opportunity to produce a site selective light-induced action, controlled by the tailored intense laser field, on atoms in molecules and clusters. The concept is illustrated by ab initio molecular dynamics simulations of the water hexamer.

  • 136.
    Usman, Muhammad
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Hallen, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Ghandi, Reza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Domeij, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Effect of 3.0 MeV helium implantation on electrical characteristics of 4H-SiC BJTs2010Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T140, s. 014012-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Degradation of 4H-SiC power bipolar junction transistors (BJTs) under the influence of a high-energy helium ion beam was studied. Epitaxially grown npn BJTs were implanted with 3.0 MeV helium in the fluence range of 10(10)-10(11) cm(-2). The devices were characterized by their current-voltage (I-V) behaviour before and after the implantation, and the results showed a clear degradation of the output characteristics of the devices. Annealing these implanted devices increased the interface traps between passivation oxide and the semiconductor, resulting in an increase of base current in the low-voltage operation range.

  • 137. Vinas, X.
    et al.
    Bhagwat, A.
    Centelles, M.
    Schuck, P.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Applications to nuclear properties of the microscopic-macroscopic model based on the semiclassical Wigner-Kirkwood method2015Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, nr 11, artikkel-id 114001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Some time ago we proposed a new microscopic-macroscopic model where the semiclassical Wigner-Kirkwood expansion of the energy up to fourth-order in. is used to compute the shell corrections in a deformed Woods-Saxon potential instead of the usual Strutinsky averaging scheme. For a set of 558 even-even nuclei computed with this new model, we found a rms deviation of 610 keV from the experimental masses, similar to the value obtained using the well-known finite range droplet model and the Lublin-Strasbourg drop model for the same set of nuclei. In this paper we analyze the alpha radioactivity in nuclei with mass number A similar to 100, finding good agreement with the available experimental results. We have also estimated spontaneous fission half-lives for superheavy nuclei in the region between Z = 102 and Z = 110. We find that our model predicts reasonably well the experimental half-lives in the considered nuclei, in spite of the fact that the fission barriers turn out to be somewhat too high.

  • 138.
    Vitos, Levente
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nilsson, J. O.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Stacking fault energy and magnetism in austenitic stainless steels2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stacking fault energies are used to illustrate the footprint of magnetism on the mechanical properties of Fe-Cr-Ni alloys forming the basis of austenitic stainless steels. We find that the usual chemical effects of alloying additions are accompanied by major magnetic effects, which stabilize the most common industrial alloy steels at normal service temperatures. We suggest that part of the uncertainties associated with the experimental data on the stacking fault energies are due to the strong concentration and temperature dependence originating from the persisting local magnetic moments.

  • 139.
    Weckmann, Armin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Wienhold, P.
    Brezinsek, S.
    Coenen, J. W.
    Kischner, A.
    Kreter, A.
    Pospieszczyk, A.
    Local Migration Studies of High-Z Metals in the TEXTOR Tokamak2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014058Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Volatile compounds of tungsten (WF6) and molybdenum (MoF6) were used as tracers of high-Z metal migration in the TEXTOR tokamak in several gas injection experiments when puffing was done through a test limiter. The experiments with W were performed prior major shut-downs, while the MoF6 was followed by the final shutdown in connection with TEXTOR decommissioning. In all cases a set of various surface probes and limiter tiles were retrieved and analysed with electron and ion beam techniques. The focus was on the local deposition in the vicinity of the gas inlet and in the inlet system. Depth profiles in the deposits and metal distribution maps clearly shown that only near the gas inlet significant amounts of Mo are deposited along the scrape-off layer flow and E×B drift directions, which could be reproduced by ERO-code modelling. Correlation between the plasma operation scenario and the deposition patterns is presented.

  • 140. Widdowson, A.
    et al.
    Alves, E.
    Ayres, C. F.
    Baron-Wiechec, A.
    Brezinsek, S.
    Catarino, N.
    Coad, J. P.
    Heinola, K.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Material migration patterns and overview of first surface analysis of the JET ITER-like wall2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Following the first JET ITER-like wall operations a detailed in situ photographic survey of the main chamber and divertor was completed. In addition, a selection of tiles and passive diagnostics were removed from the vessel and made available for post mortem analysis. From the photographic survey and results from initial analysis, the first conclusions regarding erosion, deposition, fuel retention and material transport during divertor and limiter phases have been drawn. The rate of deposition on inner and outer base divertor tiles and remote divertor corners was more than an order of magnitude less than during the preceding carbon wall operations, as was the concomitant deuterium retention. There was however beryllium deposition at the top of the inner divertor. The net beryllium erosion rate from the mid-plane inner limiters was found to be higher than for the previous carbon wall campaign although further analysis is required to determine the overall material balance due to erosion and re-deposition.

  • 141. Widdowson, A.
    et al.
    Coad, J. P.
    Alves, E.
    Baron-Wiechec, A.
    Barradas, N. P.
    Catarino, N.
    Corregidor, V.
    Heinola, K.
    Krat, S.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH.
    Impurity re-distribution in the corner regions of the JET divertor2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The International Thermonuclear Experimental Reactor (ITER) will use a mixture of deuterium (D) and tritium (T) as the fuel to generate power. Since T is both radioactive and expensive the Joint European Torus (JET) has been at the forefront of research to discover how much T is used and where it may be retained within the main reaction chamber. Until the year 2010 the JET plasma facing components were constructed of carbon fibre composites. During the JET carbon (C) phases impurities accumulated at the corners of the divertor located towards the bottom of the chamber in regions shadowed from the plasma where they are very difficult to reach and remove. This build-up of C and the associated H-isotope (including T) retention were of particular concern for future fusion reactors therefore, in 2010 JET changed the wall protection to (mainly) Be and the divertor to tungsten (W)-the JET ITER-like wall (ILW)-the choice of materials for ITER. This paper reveals that with the JET ILW impurities are still accumulating in the shadowed regions, with Be being the majority element, though the overall quantities are very much reduced from those in the C phases. Material will be transported into the shadowed regions principally when the plasma strike points are on the corner tiles, but particles typically have about a 75% probability of reflection from line-of sight surfaces, and multiple reflection/scattering results in deposition over all surfaces.

  • 142. Wu, D
    et al.
    Hellberg, Per-Erik
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Zhang, Shi-Li
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Considerations of pad compensation for on-wafer high frequency characterization of MOSFETs2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, s. 70-74Konferansepaper (Fagfellevurdert)
    Abstract [en]

    When on-wafer high frequency characterization of MOSFETs is performed, influences of the substrate coupling arising from metal bonding pads have to be considered in order to de-embed the characteristics of intrinsic transistors at high frequencies. In this work we examine different metal pad configurations used for the de-embedding procedure, i.e. pad compensation. Lumped circuit models are used to account for the effects of the metal pads and the substrate beneath. Good agreement is found between the Y-parameters of the proposed models and the measured data up to 18 GHz. With the guidance of the models we discuss designs of metal pad configurations, substrate resistivity substrate isolation and layout of MOSFETs in order to improve the accuracy of the pad compensation.

  • 143. Zeng, Hong Li
    et al.
    Hertz, John
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Roudi, Yasser
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    L-1 regularization for reconstruction of a non-equilibrium Ising model2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, nr 10, s. 105002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The couplings in a sparse asymmetric, asynchronous Ising network are reconstructed using an exact learning algorithm. L-1 regularization is used to remove the spurious weak connections that would otherwise be found by simply maximizing the log likelihood of a finite data set. In order to see how L-1 regularization works in detail, we perform the calculation in several ways including (1) by iterative minimization of a cost function equal to minus the log likelihood of the data plus an L-1 penalty term, and (2) an approximate scheme based on a quadratic expansion of the cost function around its minimum. In these schemes, we track how connections are pruned as the strength of the L-1 penalty is increased from zero to large values. The performance of the methods for various coupling strengths is quantified using receiver operating characteristic curves, showing that increasing the coupling strength improves reconstruction quality.

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