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  • 1. Gasior, P.
    et al.
    Czarnecka, A.
    Parys, P.
    Rosinski, M.
    Wolowski, J.
    Hoffman, J.
    Szymanski, Z.
    Philipps, V.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Effective laser-induced removal of co-deposited layers from plasma-facing components in a tokamak2006In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 56, p. B67-B72Article in journal (Refereed)
    Abstract [en]

    An experimental set-up and spectroscopy diagnostic method for laser-induced fuel removal and decomposition of co-deposited layers on plasma-facing components from tokamaks are described. For irradiation of a graphite limiter tile from the TEXTOR tokamak Nd:YAG 3.5-ns pulse laser with a repetition rate of 10 Hz and single pulse energy of up to 0,8 J at 1,06 mu m has been used. The spectroscopy system allowed recording of spectra in the visible wavelength range including CII and D alpha spectral lines. The evolution of CII and Da spectral lines was observed pulse-by-pulse during the co-deposit removal. The efficient ablation of the 45 mu m thick co-deposit occured after approximately 50 laser pulses.

  • 2. Krlin, L.
    et al.
    Panek, R.
    Pavlo, P.
    Petrzilka, V.
    Stockel, J.
    Svoboda, V.
    Kuhn, S.
    Tskhakaya, D.
    Tendler, Michael
    KTH, Superseded Departments, Alfvén Laboratory.
    Anomalous impurity diffusion in models of tokamak edge plasma turbulence2004In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 54, no 1-3, p. 157-163Article in journal (Refereed)
    Abstract [en]

    Using a simple spatially periodical and stationary potential as a model of electrostatic tokamak edge plasma turbulence, we have found recently [1, 2] an anomalous impurity diffusion in this regime. In this contribution, we estimate this diffusion for a more general and realistic form of the potential, which is close to the Hasegawa-Wakatani (HW) potential. As an interesting consequence of the discussed dynamics, we present, possibility of radial electric field generation in the edge turbulence regime. This effect. might play a role in tokamak scenarios with transport barriers.

  • 3.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Eltsev, Yuri
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Vortex dynamics in different magnetic field directions of untwinned YBa2Cu3O7-delta single crystals1996In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 46, no Suppl. 3, p. 1705-1706Article in journal (Refereed)
    Abstract [en]

    Current-Voltage (I-V) characteristics have been measured on an untwinned single crystal of YBa2Cu3O7-delta with the current along the b-axis and with the applied magnetic field along various crystallographic axes. Measurements with the magnetic field in the ab-plane resulted in a different qualitative behaviour of the I-V characteristics than for the field applied along the c-axis.

  • 4.
    Obara, Haruhiko
    et al.
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Andersson, Magnus
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fabrega, Lourdes
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fivat, Patrice
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Triscone, Jean-Marc
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Decroux, Michel
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fischer, Oystein
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Vortex system in coupled DyBa2Cu3O7-delta(Y0.45Pr0.55)Ba2Cu3O7-delta heterostructures1996In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 46, no SUPPL. 3, p. 1565-1566Article in journal (Refereed)
    Abstract [en]

    Transport measurements have been used to determine the vortex phase diagram (H parallel to c) of coupled heterostructures made of superconducting ultra-thin DyBa2Cu3O7-delta layers separated by semiconducting (Y0.45Pr0.55)Ba2Cu3O7-delta layers. These structures have an intermediate anisotropy between those of YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+d. The solid-to-liquid transition and the flux dynamics have been investigated as a function of the total sample thickness d. Analyses of the parameters describing the thermally activated dissipation in the solid and liquid phases reveal a field induced crossover characterized by two fields, H-on(T) and H*>H-on. We discuss the meaning of these features and their relationship with results in bulk high temperature superconductors.

  • 5. Serianni, G.
    et al.
    Antoni, V.
    Bergsåker, Henric
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, P.
    Drake, James R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Spolaore, M.
    Satherblom, H. E.
    Vianello, N.
    Electrostatic fluxes and plasma rotation in the edge region of EXTRAP-T2R2001In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 51, no 10, p. 1119-1127Article in journal (Refereed)
  • 6.
    Sigurdsson, Gunnar
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Silvestrov, Sergei D.
    Graded quasi-Lie algebras of Witt type2006In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 56, no 10-11, p. 1287-1291Article in journal (Refereed)
    Abstract [en]

    In this article, we introduce a new class of graded algebras called quasi-Lie algebras of Witt type. These algebras can be seen as a generalization of other Witt-type algebras like Lie algebras of Witt type and their colored version, Lie color algebras of Witt type.

  • 7. Usachev, A.
    et al.
    Zobnin, A.
    Petrov, O.
    Fortov, V.
    Thoma, M.
    Kretschmer, M.
    Ratynskaia, Svetlana V.
    Quinn, R.
    Hoefner, H.
    Morfill, G.
    The project Plasmakristall-4 (PK-4) - a dusty plasma experiment in a combined dc/rf(i) discharge plasma under microgravity conditions2004In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 54, p. C639-C647Article in journal (Refereed)
    Abstract [en]

    The PK-4 experiment is a continuation of the successful dusty plasma experiments PK-1, PK-2 and PK-3 conducted on board of the orbital space stations Mir and IS S (International Space Station). The aim of the PK-4 experiment is an investigation of physical processes in complex (dusty) plasmas under microgravity conditions in a combined dc/rf discharge plasma.

  • 8. Van Oost, G.
    et al.
    Gunn, J. P.
    Melnikov, A.
    Stockel, J.
    Tendler, Michael
    KTH, Superseded Departments, Alfvén Laboratory.
    The role of radial electric fields in the tokamaks TEXTOR-94, CASTOR, and T-102001In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 51, no 10, p. 957-975Article in journal (Refereed)
    Abstract [en]

    Radial electric fields (E-r) and their role in the establishment of edge transport barriers and improved confinement have been studied in the tokamaks TEXTOR-94 and CASTOR, where E-r is externally applied to the plasma in a controlled way using a biased electrode, as well as in the tokamak T-10 where an edge transport barrier (H-mode) is obtained during electron-cyclotron resonance heating (ECRH) of the plasma. The physics of radial currents was studied and the radial conductivity in the edge of TEXTOR-94 (R = 1.75 m, a = 0.46 m) was found to be dominated by recycling (ion-neutral collisions) at the last closed flux surface (LCFS) and by parallel viscosity inside the LCFS. From a performance point of view (edge engineering), such electrode biasing was shown to induce a particle transport barrier, a reduction of particle transport, and a concomitant increase in energy confinement. An H-mode-like behaviour can be induced both with positive and negative electric fields. Positive as well as negative electric fields were shown to strongly affect the exhaust of hydrogen, helium, and impurities, not only in the H-mode-like regime. The impact of sheared radial electric fields on turbulent structures and flows at the plasma edge is investigated on the CASTOR tokamak (R = 0.4 m, a = 0.085 m). A non-intrusive biasing scheme that we call separatrix biasing is applied whereby the electrode is located in the scrape-off layer (SOL) with its tip just touching the LCFS. There is evidence of strongly sheared radial electric field and E x B flow, resulting in the formation of a transport barrier at the separatrix. Advanced probe diagnosis of the edge region has shown that the E x B shear rate that arises during separatrix biasing is larger than for standard edge plasma biasing. The plasma flows, especially the poloidal E x B drift velocity, are strongly modified in the sheared region, reaching Mach numbers as high as half the sound speed. The corresponding shear rates (approximate to5 x 10(6) s(-1)) derived from both the flow and electric field profiles are in excellent agreement and are at least an order of magnitude higher than the growth rate of unstable turbulent modes as estimated from fluctuation measurements. During ECRH in the tokamak T-10 (R = 1.5 m, a = 0.3 m), a regime of improved confinement is obtained with features resembling those in the H-mode in other tokamaks. Using a heavy ion beam probe, a narrow potential well is observed near the limiter together with the typical features of the L-H transition. The time evolution of the plasma profiles during L-H and H-L transitions is clearly correlated with that of the density profile and the formation of a transport barrier near the limiter, The edge electric field is initially positive after the onset of ECRH. It changes its sign during the L-H transition and grows till a steady condition is reached. Similar to the biasing experiments in TEXTOR-94 and CASTOR, the experimentally observed transport barrier is a barrier for particles.

  • 9. Van Oost, G.
    et al.
    Tendler, Michael
    KTH, Superseded Departments, Alfvén Laboratory.
    Stockel, J.
    Role of electric field in plasma confinement and exhaust2000In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 50, p. 11-24Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical aspects of the role of electric fields in plasma confinement and exhaust are overviewed. The history of the discovery of the importance of electric fields in plasmas is depicted. The correlation between radial electric fields and plasma rotation is outlined. The concept of E x B flow velocity shear suppression is explained and modelled. Edge polarization results on the CASTOR tokamak are presented. Recent results in the formation of internal transport barriers are summarized.

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