Ray tracing model of the auroral kilometric radiation generation in the 3-D plasma cavity

Propagation and amplification of the auroral kilometric radiation (AKR) in a three-dimensional plasma cavity is investigated using the approximation of the geometrical optics, and taking into account both the slightly relativistic electrons propagating inside a cavity and the background cold electrons. It is shown that the global magnetic field inhomogeneity plays a key role in a wave escape from a thin plasma cavity. The main contribution to the AKR spectrum is made by waves initially generated with the component of group velocity directed to the Earth and with the optimum relationship between the wave vector components, controlling the value of the linear grow rate and duration of the ray lifetime inside a source

Thin Plasma Cavities as a Source of the Auroral Kilometric Radiation

International audienceThe investigation of the cyclotron maser instability in sources of finite perpendicular extension separated from the denser and cold surrounding plasma by sharp density gradients is made within the waveguide approximation. The general dispersion equation of wave propagation and amplification is obtained and solved numerically for different regimes. It is found that the growth rate of oblique eigenmode increases with the increasing of the perpendicular component of the wave vector directed along cavity boundaries. The structure of electromagnetic fields inside the source region is studied and changes of the wave polarization are discussed

Auroral kilometric radiation from a nonstationary thin plasma cavity

Results obtained using a waveguide model of the AKR generation in thin plasma cavities are presented. Taking into account the occurrence of low frequency plasma motion in the regions of the AKR generation, we have considered a wave escape from a thin plasma cavity with adiabatically slowly varying width, and show that there can exist localized regions of instability from which the extraordinary X-mode waves, growing in time, can be radiated outwards. It has been found that waves, propagating quasi-tangentially to the source frontiers, have the maximum growth rate and escape outward most efficiently, which is in accordance with experimental observations

Thin Plasma Cavities as a Source of the Auroral Kilometric Radiation

International audienceThe investigation of the cyclotron maser instability in sources of finite perpendicular extension separated from the denser and cold surrounding plasma by sharp density gradients is made within the waveguide approximation. The general dispersion equation of wave propagation and amplification is obtained and solved numerically for different regimes. It is found that the growth rate of oblique eigenmode increases with the increasing of the perpendicular component of the wave vector directed along cavity boundaries. The structure of electromagnetic fields inside the source region is studied and changes of the wave polarization are discussed

Kelvin-Helmholtz instability for a bounded plasma flow in a longitudinal magnetic field

International audienceKelvin-Helmholtz MHD instability in a plane three-layer plasma is investigated. A general dispersion relation for the case of arbitrarily orientated magnetic fields and flow velocities in the layers is derived, and its solutions for a bounded plasma flow in a longitudinal magnetic field are studied numerically. Analysis of Kelvin-Helmholtz instability for different ion acoustic velocities shows that perturbations with wavelengths on the order of or longer than the flow thickness can grow in an arbitrary direction even at a zero temperature. Oscillations excited at small angles with respect to the magnetic field exist in a limited range of wavenumbers even without allowance for the finite width of the transition region between the flow and the ambient plasma. It is shown that, in a low-temperature plasma, solutions resulting in kink-like deformations of the plasma flow grow at a higher rate than those resulting in quasi-symmetric (sausage-like) deformations. The transverse structure of oscillatory-damped eigenmodes in a low-temperature plasma is analyzed. The results obtained are used to explain mechanisms for the excitation of ultra-low-frequency long-wavelength oscillations propagating along the magnetic field in the plasma sheet boundary layer of the Earth’s magnetotail penetrated by fast plasma flows