Speaker
Egor Dmitrievich Gospodchikov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1069.pdf
Spectrum broadening and degradation of the O-X mode coupling
efficiency due scattering of a microwave beam on plasma density
fluctuations
E. Gospodchikov1, T. Khusainov1, A. Shalashov1, A. Köhn2
1
Institute of Applied Physics RAS, Nizhniy Novgorod, Russia
2
IGVP, University of Stuttgart, Stuttgart, Germany
We discuss the tunnelling of quasi-optical wave beams through the evanescent region near
the plasma cut-off in magnetized plasmas with density fluctuations: so called ordinary(O)
and extraordinary(X) mode coupling. The primary influence of density fluctuations on the
O-X mode coupling efficiency is due to a small-angle scattering of a microwave beam
along the whole trace of its propagation, while the influence of the fluctuations inside the
localised coupling region may be neglected [1]. In this paper model is proposed that
describes the effect of a random modulation of a wave phase induced by the fluctuations
along the propagation path on the efficiency of linear O-X mode coupling in a two-
dimensional geometry that suits well the toroidal magnetic conditions [2]. An analytical
formula is derived that relates the mean coupling efficiency and the phase correlation
function of a random wave beam. Thresholds are found for the correlation length of the
random phase and the length of the beam path, above which the density fluctuations
become the dominant effect. The peculiar effects of two-dimensional geometry of mode
coupling region [3], including the magnetic field-line curvature [4] and the magnetic
surface curvature [5] are shown to be important even in the presents of fluctuations. The
results of the analytical study are verified with full-wave numerical simulations.
[1] A. G. Shalashov, E. D. Gospodchikov, PPCF 56 125011 (2014).
[2] T. A. Khusainov, E.D. Gospodchikov, A.G. Shalashov, JETP 126 366 (2018).
[3] E.D. Gospodchikov, A.G. Shalashov, E.V. Suvorov, PPCF 48 869 (2006).
[4] A.G. Shalashov, E. D. Gospodchikov, PPCF 52 115001 (2010).
[5] E. D. Gospodchikov, T. A. Khusainov, A. G. Shalashov, PPCF 54 045009 (2012).
