Plasma Physics(DPP)
Physique des plasmas (DPP)

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Akira HIROSE
University of Saskatchewan

Anomalous Electron Thermal Conductivity in Tokamaks

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The electron thermal diffusivity in tokamaks has been known to be anomalously high since the beginning of the tokamak research. As the anomalous ion thermal diffusion is caused by an ion temperature gradient, it is natural to seek instabilities driven by electron temperature gradient (ETG). A toroidicity driven ETG mode has been revisited in tokamak stability analysis based on a fully kinetic, electromagnetic integral equation code recently developed in the Laboratory. The ETG mode is characterized by short wavelengths which can be comparable with the Debye length and charge neutrality often assumed in the analysis of the ETG mode breaks down. For typical tokamak discharge parameters, the maximum growth rate occurs at a wavenumber comparable with the Debye wavenumber. The growth rate is of the order of the electron transit frequency and is proportional to square root of plasma beta factor. The electron thermal diffusivity based on simple mixing length estimate is large enough to be relevant to the experimentally observed values, and it increases with the plasma minor radius^[1]. ^[1] A. Hirose, Phys. Rev. Lett. 92, 025001 (2004).