Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

Mode-conversion of the extraordinary wave at the upper hybrid resonance in the presence of small-amplitude density fluctuations

“…BBS occurs when the resonance condition k n = 2k(x) ≈ 2 √ γ R is satisfied, and constructive interference in the reflected wave pattern results. It was originally discovered in the context of x-ray crystallography [62], but has gained renewed interest in the hydrodynamics community through the design of Bragg breakwaters to protect shorelines [63], and in the plasma physics community through studies on reflectometry and the O-X-B mode-conversion in the presence of turbulence [64,65,66]. Near the BBS resonance, the perturbative approach breaks down, and the reflection coefficient provided by equation 41 is not necessarily bounded by 1.…”

The effect of spectrum broadening on the O–X mode coupling due scattering of a microwave beam on plasma density fluctuations

“…At this, the so-called enhanced scattering, characteristic of the plasma cutoff [14,15], does not appear when the O mode is strongly coupled to the X mode. This rather unexpected result was first mentioned in [11] among other features of wave propagation near the fluctuating point of O-X mode degeneracy, while [12] was specially focused on physical explanation of this particular feature of back-scattering. Thus, these studies suggest that perturbations of the averaged O-X coupling efficiency due to fluctuations inside the localized coupling region are usually negligible, and the main effect of fluctuations is accumulated outside the coupling region.…”

“…Such scattering leads to an additional phase modulation of the wave beam, but not to the refraction or reflection of the beam as a whole. For this process, the coupling region is not distinguished, i.e., the scattering occurs here with the same efficiency as outside (no enhanced scattering [12]). The dimensions of the coupling region are, as a rule, much smaller than the total propagation path of the beam.…”

“…A significant influence of density fluctuations, inherent of hot magnetized plasma in toroidal magnetic traps, on the process of linear transformation was first noted in [4], where a simple phenomenological model of this phenomenon was considered. Recently, by a more rigorous analysis, this picture has been substantially revised [11][12][13]. As a result of solving the truncated Maxwell equations in the linear interaction region in the presence of density fluctuations for the parameters corresponding to modern experiments, it was established that the dominant effect in the O-X coupling efficiency is due to small-angle scattering of the wave beam on the fluctuations along the propagation path towards the cutoff.…”

“…The previous results were obtained based on the assumption that either average gradients of the plasma density and magnetic field modulus are parallel [11,12] or the homogeneous magnetic field [13]. That is, a regular plasma has always been described in the framework of a onedimensional approximation, while fluctuations resulted in three-dimensional perturbations of the one-dimensional geometry.…”