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@BOOK{Kreter:42846,
      author       = {Kreter, Arkadi},
      title        = {{L}adungsaustauschspektroskopie mit {H}ilfe eines
                      {W}asserstoffdiagnostikstrahls am {T}okamak {TEXTOR}-94},
      volume       = {3860},
      issn         = {0944-2952},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-42846, Juel-3860},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {96 p.},
      year         = {2001},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {In this work the energy and impurity transport was
                      investigated by means of the active chargeexchange
                      recombination spectroscopy (CXRS). CXRS is a method to
                      determine the ion temperature, plasma rotation and impurity
                      density both space and time-resolved . It is based on the
                      investigation of the spectral shape of the lines, which are
                      emitted by the impurity ions after the CX processes with the
                      neutral particles . The source of the neutral particles are
                      high-energy beams (e.g. heating beams), which penetrate
                      deeply into the plasma and therefore enable the measurements
                      over the entire plasma radius. During this work a new CXRS
                      diagnostics was installed at TEXTOR-94. The principal part
                      of this diagnostics is the diagnostic hydrogen beam RUDI.
                      The RUDI injector ensures an equivalent neutral current of 1
                      .1 A with an energy of 50 keV and a pulse length of 4 s,
                      modulated with 500 Hz. The observation system covering the
                      whole beam path and a low divergence of 0.6° of the RUDI
                      beam lead to a good space resolution. Measurements using a
                      modified CXRS diagnostics at the heating beam were performed
                      for the characterisation of the plasma edge, particularly in
                      discharges with impurity seeding and improved energy
                      confinement (RI-mode) . With the measurements of the ion
                      temperature and plasma rotation profiles it was proven, that
                      in the RI-mode there is no transport barrier at the plasma
                      edge, which is typical for another regime with the improved
                      confinement, the H-mode. The ratio of the ion and electron
                      temperature at the plasma edge varies between 4 at the low
                      and 1 .5 at the high densities . The ratio TilT, becomes
                      larger with increasing radiation level, because the
                      electrons are cooled directly via inelastic collisions with
                      the impurity ions . A correlation between the measured edge
                      parameters and the global confinement characteristics was
                      observed: the confinement degradation leads to the higher
                      neutral particle densities at the edge, which slow down the
                      toroidal rotation influenced by the flows in the scrape-off
                      layer. Regarding CXRS the most important advantage of the
                      diagnostic beam in relation to the heating beam is the
                      possibility to measure under all discharge conditions.
                      Measurements with RUDI took place to a large extent under
                      conditions of ohmic plasma heating: the energy balance of
                      ions and electrons was investigated for different plasma
                      currents and densities ; in high density discharges the
                      transition to improved ohmic confinement (IOC) was observed
                      after switching off the external gas flow. In the standard
                      high density ohmic plasmas (saturated ohmic confinement -
                      SOC) the confinement time is independent of the plasma
                      density . In contrast, it scales in the IOC regime linearly
                      with the density . The SOC-IOC transition was investigated
                      regarding the influence of the toroidal ITG instability
                      driven by the ion temperature gradient. On the basis of the
                      measured ion temperature distributions the q;-parameter
                      (ratio of the density and ion temperature decay lengths) and
                      the growth rate of the ITG instability were calculated. The
                      ITG mode is destabilised, if ih is larger then a critical
                      value depending on the scale length of the density profile.
                      After the SOC-IOC transition i1i lies in a noticeably
                      smaller radial region over the critical value. As the
                      result, the IOC regime is characterised by a clear reduction
                      of the growth rate y1To. The steepening of the plasma
                      density profile after the reduction of the external gas flow
                      leads to the suppression of the ITG instability and to the
                      improvement of the confinement in the IOC regime. First
                      measurements of the impurity densities in ohmic and
                      additionally heated discharges were performed. Densities of
                      C6+, Nel°+, Ney+, Nex' and Ox+ were determined. The
                      measured density profiles show qualitatively a good
                      agreement in their radial shape with the profiles calculated
                      by the impurity transport code RITM. However, there are
                      relatively large quantitative deviations of up to 50 $\%,$
                      which can be explained by inaccurate CX rate coefficients
                      for the not completely ionised particles. For clarifying
                      these discrepancies additional measurements of the impurity
                      densities under different plasma conditions are needed.},
      cin          = {IPP-1 / IPP-2},
      cid          = {I:(DE-Juel1)VDB27 / I:(DE-Juel1)VDB28},
      pnm          = {Teilchen- und Energietransport in der Plasmarandschicht},
      pid          = {G:(DE-Juel1)FUEK48},
      typ          = {PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/42846},
}