RUDI GAELZER

Nonlinear interactions of tenuous electron beam, background, unmagnetized plasma, and self-consistently generated Langmuir and ion-sound waves are analyzed in the framework of plasma weak turbulence kinetic theory. Full numerical solutions of the complete weak turbulence equations are obtained for the first time, which show the familiar plateau formation in the electron beam distribution and concomitant quasi-saturation of primary Langmuir waves, followed by fully nonlinear processes which include three-wave decay and induced-scattering processes. A detailed analysis reveals that the scattering off ions is an important nonlinear process which leads to prominent backscattered and long-wavelength Langmuir wave components. However, it is found that the decay process is also important, and that the nonlinear development of weak Langmuir turbulence critically depends on the initial conditions. Special attention is paid to the electron-to-ion temperature ratio, Te/Ti, and the initial perturbation level. It is found that higher values of Te/Ti promote the generation of backscattered Langmuir wave component, and that a higher initial wave intensity suppresses the backscattered component while significantly enhancing the long-wavelength Langmuir wave component.

The derivation of explicit exprEssions for the effective dielectric tensor to be utilized in the dispersion relation for weakly inhomogeneous Plasmas is discussed. The general exprEssions obtained are useful for situations with simultaneous existence of weak inhomogeneities in density and magnetic field. The particular case of a Maxwellian distribution in velocity space for the electron population is discussed, and relatively compact exprEssions for the dielectric tensor are obtained which depend on the inhomogeneous Plasma dispersion function introduced by [Gaelzer et al., Phys. Rev. E55, 5859 (1997)] and ultimately on the well-known Fried-Conte function and its derivatives.

We investigate propagation and amplification of the auroral kilometric radiation over the geomagnetic poles using a particular model for the physical parameters in the auroral zone, which takes into account density gradients perpendicular to the geomagnetic field. The propagation of the waves is investigated with the canonical set of equations of the geometrical optics, taking into account thermal effects and considering both the energetic and the background electron populations, with the components of the dielectric tensor calculated in the locally homogeneous plasma approximation. It is shown that the spatial scale of inhomogeneity perpendicular to the magnetic field is an important factor in the amplification, although less favorable than indicated by previous studies using the method of Poeverlein to obtain the trajectory of the radiation.

We investigate amplification of the auroral kilometric radiation over the geomagnetic poles. The physical parameters needed for the calculation are obtained from a particular model that approximately reproduces the conditions in the auroral zone, taking into account density gradients perpendicular to the geomagnetic field and also the parallel magnetic field gradient. The components of the dielectric tensor are calculated in the locally homogeneous plasma approximation, and the dispersion relation is exactly solved with all harmonics and powers of the Larmor radius needed for the convergency of the solution. We also make a ray tracing study in the geometrical optics approximation, using the method of Poeverlein. The ray tracing study shows that the spatial scale of inhomogeneity, perpendicular to the magnetic field, is a very important factor in the amplification and that the distance to obtain a given amplification can be substantially reduced when the density gradient is increased.