A model for anomalous thermal diffusivity in tokamaks

Abstract

It has been recently pointed out that a certain function F of the plasma density, n(r), and the electron temperature gradient relative to the density gradient, eta /sub e/(r), reproduces well the radial profiles of chi /sub e/ (electron thermal diffusivity) in several tokamaks with various heating modes. Plots are shown of F with n=10/sup 19//m/sup 3/ and the experimentally deduced chi /sub e/ (m/sup 2//s) in three different modes in JET: ohmic, ohmic+ICRH, and ohmic+NBI. The F and chi /sub e/ profiles agree rather well. The factor 1+ eta /sub e/, which appears in the numerator of F, is proportional to the pressure gradient, which may provide a source for drift-type instability. The electron temperature gradient, which appears in the denominator, is possibly due to the nonlinear stabilization of drift-type modes by temperature gradient.<>