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Abstract

The Tore Supra database of fast wave electron heating discharges is analysed with respect to the role of the critical electron temperature gradient. The experimental evidence for the critical gradient is presented from power balance thermal flux q(e)(anadeltaT(e)) relation extrapolated to zero in the measured gradient anadeltaT(e). The fluctuation spectra are also known to extrapolate to low levels versus anadeltaT(e). The inferred critical gradient (anadeltaT(e))(c) is defined by the offset linear extrapolation of the thermal flux to zero values.

The relative deviations of the normalized heat fluxes as a function of the excess of the temperature gradient beyond the critical gradient give one method of assessing the agreement between the models and the data. A second method is the predictive studies in which the transport codes are used to investigate the impact of the critical gradient at low and high radio frequency power levels with the model thermal diffusivities.

The dominant dependence of the inferred critical temperature gradient is its proportionality to the magnetic shear as expected from the robust electron Landau damping on thermal electrons in electron temperature gradient turbulence. The evidence for the electrostatic density independent thermal diffusivity scaling versus the finite beta electromagnetic density dependent thermal diffusivity is shown in some detail. The results strongly favour the electromagnetic turbulent diffusivity formula.

Additional information

Authors: HOANG G T, EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR);BOURDLLE C, EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR);GARBET X, EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR);OTTAVIANI M, EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR);HORTON W, Institute for Fusion Studies, University of Texas at Austin (US);HU B, Institute for Fusion Studies, University of Texas at Austin (US)
Bibliographic Reference: An article published in: Physics of Plasmas -Volume 10, Issue 2, (February 2002), pp.405-412
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/10.1063/1.1534113
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