Experimental data are presented that are consistent with the hypothesis that anomalous rf absorption in helicon sources is due to electron scattering arising from parametrically driven ion-acoustic waves downstream from the antenna. Also presented are ion temperature measurements demonstrating anisotropic heating (T( perpendicular)>T(parallel)) at the edge of the discharge. The most likely explanation is ion-Landau damping of electrostatic slow waves at a local lower-hybrid-frequency resonance.
The linear and renormalized nonlinear kinetic theory of drift instability of plasma shear flow across the magnetic field, which has the Kelvin's method of shearing modes or so-called non-modal approach as its foundation, is developed. The developed theory proves that the time-dependent effect of the finite ion Larmor radius is the key effect, which is responsible for the suppression of drift turbulence in an inhomogeneous electric field. This effect leads to the non-modal decrease of the frequency and growth rate of the unstable drift perturbations with time. We find that turbulent scattering of the ion gyrophase is the dominant effect, which determines extremely rapid suppression of drift turbulence in shear flow.
Temporal evolution of linear drift waves in a collisional plasma with a homogeneous shear flow is treated analytically. The explicit solutions for the linearized Hasegawa–Wakatani system of equations, as well as for linearized Hasegawa–Mima equation, are obtained for this case on the basis of the nonmodal approach. In the weak-collision regime, the homogeneous shear flow is found to be a factor impeding the development of the ordinary modal resistive drift instability. This instability is excited only in the case of a weak velocity shear. For a stronger shear, the nonmodal effects, such as the blocking of drift wave packets and the linear transformation of drift waves into convective cells, determine the temporal evolution of drift-like perturbations. A nonmodal solution is found in the limit of strong collisions or sufficiently strong flow shear. The solution at the asymptotically large time possesses a convective-cell pattern.
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