MHD MODEL INCLUDING SMALL-SCALE PERTURBATIONS IN A PLASMA WITH TEMPERATURE-VARIATIONS

The possibility is studied of using a hydrodynamic model to describe a magnetized plasma with density and temperature variations on scales t hat are arbitrary with respect to the ion Larmor radius. It is shown t hat the inertial component of the transverse ion thermal flux should b e taken into account. This component is found from the collisionless k inetic equation. It can also be obtained from the equations of the Gra d type. A set of two-dimensional hydrodynamic equations for ions is ob tained with this component taken into account. These equations are use d to derive model hydrodynamic expressions for the density and tempera ture variations. It is shown that, for large-scale perturbations (when the wavelengths are longer than the ion Larmor radius), the expressio ns derived coincide with the corresponding kinetic expressions and, fo r perturbations on sub-larmor scales (when the wavelengths are shorter than the Larmor radius), they agree qualitatively. Hydrodynamic dispe rsion relations are derived for several types of drift waves with arbi trary wavenumbers. The range of applicability of the MHD model is dete rmined from a comparison of these dispersion relations with the kineti c ones. It is noted that, on the basis of the results obtained, drift effects can be included in numerical MHD codes for studying plasma ins tabilities in high-temperature regimes in tokamaks.