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  • 1
    Electronic Resource
    Electronic Resource
    Influence of resonant helical windings on the mirnov oscillations in a small tokamak (1988)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 10 (1988), S. 1193-1198 
    Details
    ISSN: 0392-6737
    Keywords: Plasma equilibrium and confinement ; Plasma diagnostic techniques and instrumentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si è studiata in via sperimentale l’influenza delle perturbazioni elicoidali risonanti sul plasma confinato dal piccolo Tokamak TBR-1. Si sono potute facilmente ottenere forti attenuazioni delle oscillazioni di Mirnov attivando differenti avvolgimenti elicoidali risonanti. Si sono ripristinate ampiezze di queste oscillazioni nel momento in cui è terminata la perturbazione elicoidale.
    Abstract: Резюме Экспериментально исследуется влияние резонанснЫх спиралевиднЫх возмущений на плазму, удерживаемую в малом токамаке TBR-I. Можно легко получить сильное затухание осцилляций Мирнова с помощью различнЫх резонанснЫх спиралевиднЫх обмоток. АмплитудЫ этих колебаний восстанавливаются, когда спиралевиднЫе возмущения вЫключаются.
    Notes: Summary The influence of resonant helical perturbations on the plasma confined by the small tokamak TBR-1 was experimentally investigated. Strong attenuations of the Mirnov oscillations could be easily obtained by activating different resonant helical windings. The amplitudes of these oscillations were restored as the helical perturbation ended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02455863
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  • 2
    Electronic Resource
    Electronic Resource
    Onset of chaotic field line trajectories in tokamaks (1992)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 14 (1992), S. 695-704 
    Details
    ISSN: 0392-6737
    Keywords: Plasma equilibrium and confinement ; Plasma devices and applications ; Waves ; oscillations ; and instabilities in plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The onset of chaotic field line trajectories on tokamak plasmas perturbed by external resonant helical currents has been investigated. The spatial distribution of field lines is obtained integrating numerically the differential equations for the perturbed field lines and investigating the Poincaré maps characteristic of these fields. Several algorithms have been computed to identify the transition to large-scale stochasticity for this quasi-integrable dynamical system, which, for a given m.h.d. equilibrium, is determined by the enhancement of the coupling between the helical perturbation and the toroidicity, as the helical current increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02451716
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of disruptions in tokamak plasma under the influence of resonant helical magnetic fields (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 807-821 
    Details
    ISSN: 0392-6737
    Keywords: Plasma flow ; magnetohydrodynamics ; PACS 52.70 ; Plasma diagnostic techniques and instrumentation ; Fourier analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Disruptive instabilities were investigated in the small-tokamak TBR-1 during the application of resonant helical magnetic fields created by external helical windings. Indications were found that the main triggering mechanism of the disruption was the rapid increase of them=2/n=1 mode which, apparently after reaching a certain amplitude, interacts with other resistive modes: the internal 1/1 mode in the case of a major disruption, or with higherm components, as the 3/1 or 4/1, in the case of minor disruptions. After the coupling, the growth of the associated islands would create a chaotic field line distribution in the region between the corresponding rational magnetic surfaces which caused the gross particle transport and, finally, destroyed the confinement. In addition, investigations on higherZ eff discharges in which a mixture of helium and hydrogen was used resulted in much more unstable plasmas but apparently did not alter the basic characteristics of the disruptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457314
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  • 4
    Electronic Resource
    Electronic Resource
    Scrape-off layer intermittency in the Castor tokamak (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 846-853 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spatial–temporal intermittency of floating potential and ion saturation current fluctuations is analyzed by using data obtained from two probes arrays in the scrape-off layer of the CASTOR tokamak [Proceedings of the 1996 International Conference on Plasma Physics (Nagoya) (International Atomic Energy Agency, Vienna, 1997), Vol. I, p. 322]. For these ion saturation current fluctuations with non-Gaussian probability density functions, a conditional averaging analysis shows coherent structures with correlation lengths and lifetimes larger for larger amplitude conditions. Nevertheless, there is no evidence of such large structures in the potential fluctuations. Furthermore, wavelet transforms are used to analyze these nonstationary fluctuations and obtain details not observed with the Fourier technique. So, examining wavelet power and coherence spectra, strong intermittency is found for both kinds of fluctuations, in a time scale two orders of magnitude higher than that observed in the conditional analysis. Moreover, during the discharges the observed wavelet quadratic coupling alters intermittently for some low-frequency components. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873324
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental analysis of mode coupling and plasma turbulence induced by magnetic fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3567-3572 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wavelet spectrum and bispectrum techniques are applied to study the development of temporal turbulence induced by a confinement toroidal magnetic field in a toroidal magnetoplasma created by radio frequency waves. For low magnetic fields the plasma is roughly uniform and the analyzed electrostatic linear frequency spectra are essentially determined by the driven radio frequencies. However, by increasing the toroidal magnetic field, gradients in the plasma radial profiles and broader frequency spectra are observed. Thus, spectral components with frequencies higher than those injected in the plasma are excited. Moreover, this variation of magnetic field also induces nonlinear phase coupling between low frequency coherent peaks and continuous high frequency spectral components. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1286864
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of resonant magnetic perturbations on plasma edge turbulence (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 329-336 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work reports alterations on plasma-edge equilibrium profiles and on edge turbulence, and anomalous transport induced by resonant perturbing magnetic fields in the TBR (Brazilian Tokamak) tokamak [J. Fusion Energy 12, 295 (1993)]. Thus, these perturbations have reduced the equilibrium parameters and the spectral power of the fluctuations and enhanced their phase velocity. They have also reduced the particle flux at the plasma edge. All these electrostatic edge parameters have been computed by taking into account temperature fluctuation corrections. Although the perturbation slightly affected just the linear correlation between electrostatic fluctuations, its bispectral analysis shows a reduction of the quadratic mode coupling. Furthermore, the energy transferred between different spectral components, with and without the magnetic perturbation, did not have the same direction for all fluctuations. Finally, the normal probability distribution functions of the fluctuations show significant non-Gaussian features, although the fluctuating potential distribution became near Gaussian with the magnetic perturbation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872093
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature fluctuations and plasma edge turbulence in the Brazilian tokamak TBR (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 971-977 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To investigate the tokamak turbulence, a set of Langmuir probes and a triple probe have been designed and used in the TBR [J. Fusion Energy 12, 529 (1993)] to measure average and fluctuating values of density, potential, and temperature of the plasma edge. The obtained results showed a significant influence of the temperature fluctuations in the transport parameters. Namely, taking into account this influence, the density and plasma potential power spectra were obtained, and the turbulence parameters reevaluated. Furthermore, the computed cross-power-spectra showed appreciable linear correlation, and the cross-bispectra showed a quadratic mode coupling between temperature fluctuations and other quantities. Significant bicoherence between these fluctuations was observed. Finally, for a fluctuation monitored at two probe points, no preferential direction for energy cascading was detected. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871802
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  • 8
    Electronic Resource
    Electronic Resource
    Recurrence in plasma edge turbulence (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4455-4462 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Common statistics of turbulent electrostatic fluctuations observed at the plasma edge and scrape-off layer are analyzed in three tokamak devices that have different configurations. The statistics of experimental data collected using fixed sampling time is the same than the statistics of the time for which the oscillation return to a specified reference interval of values. This observation, in addition to the finding of power-scaling laws for some average quantities with respect to either the sampling time or the size of the reference interval, suggests that turbulence on tokamaks have recurrent characteristics, typical of a recurrent chaotic low-dimensional system. Furthermore, the first Poincaré recurrence time and other dynamical tools are used to simulate the mentioned fluctuation statistical properties. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1401117
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  • 9
    Electronic Resource
    Electronic Resource
    A complex probe for measurements of turbulence in the edge of magnetically confined plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4418-4423 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: To improve the turbulence characterization and the estimation of the transport processes at the plasma edge, we designed and installed, in the Brazilian tokamak (TBR), a complex probe that consisted of five single Langmuir probes, a four-channel triple probe, and magnetic probes. In this work, we describe in detail this diagnostic system and present experimental examples of simultaneously measured plasma parameters and electrostatic and magnetic turbulent fluctuations in the TBR tokamak. This procedure permits to investigate any coupling between these two kinds of oscillations. Furthermore, our results confirmed that corrections due to electron temperature fluctuations are relevant for turbulence characterization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148406
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  • 10
    Electronic Resource
    Electronic Resource
    Time-resolved analysis of Mirnov oscillations (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3710-3715 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We discuss the application of time-resolved spectral analysis to interpret the magnetohydrodynamic or Mirnov oscillations in tokamaks. As an example, the technique is applied to analyze the Mirnov oscillations measured in the small tokamak TBR-1 with and without external helical perturbations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143602
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