Impact of poloidal curvature on linear mode conversion of quasi-optical wave beams in tokamak plasmas

Abstract

A theory of ordinary and extraordinary wave coupling in the electron cyclotron frequency range in inhomogeneous magnetized plasmas of a toroidal magnetic trap is reconsidered. Reduced wave equations are studied taking into account the poloidal curvature of the magnetic flux surfaces in a tokamak geometry. Based on these equations, the wave field distributions in the vicinity of the coupling region are found in a semi-analytical form. Non-one-dimensional effects of the flux surface curvature on the mode-conversion efficiency in tokamak plasmas are identified and analyzed.

Antenna system analysis and design for automatic detection and real-time tracking of electron Bernstein waves in FTU

“…Both lines can be used as launching and receiving antenna, and a symmetric range of positive and negative values of N can be reached by the beam. Such a symmetric configuration makes this launcher an ideal test-bed for experiments aimed at measuring the asymmetric effects foreseen by multidimensional models of O-X conversion [17,22,23], based on a realistic description of magnetic and density gradients in the plasma. Such asymmetries are not expected to be highlighted by comparing different shots, since the level of reproducibility of the plasma parameters is not enough to measure the small differences in the transmission efficiency (only a few percent of the injected power) predicted by these models.…”

“…This should allow more tolerance in the line of sight for EBW detection, although the broadening occurs at the expense of the absolute coupling efficiency, which becomes lower than in the case of plane waves. The estimations of the coupling efficiency carried out with the FTU parameters for a beam-like field distribution are strongly dependent on the model used for the calculations and range from about 15% to a maximum level of 65% [8,9,17].…”

Feasibility study of O–X coupling for overdense plasma heating through O–X–B mode conversion in FTU

“…Concerning the future prospects of the work on the theoretical side, the application to FTU of a new computational tool for the simulations of the O-X-B heating is being considered. In this tool, the predictions of the theory applied in section 3.2 (still under improvement [32,33]), valid in the coupling region, will be linked analytically to those of a quasi-optical beam tracing code [34], used outside the cutoff layer. This allows us to evaluate mode conversion with an approach similar to full-wave but faster, since analytic, and in the FTU case this would represent an alternative to fullwave codes [35], that turn out to be more complicated from a computational point of view, dealing with a frequency wave as high as 140 GHz.…”

3D Full-Wave modelling and EC mode conversion in realistic plasmas

“…Refs. [10][11][12] suggest that conversion can be improved by a careful design of the beam wavefront. In this report we pursue an alternative optimisation strategy.…”