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Title: geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff

Abstract

This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density n e(r), which will modify the wave propagation in the direction of the gradient rn e(r).

Authors:
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1352403
Report Number(s):
LA-UR-17-23030
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; electromagnetic wave plasma

Citation Formats

Light, Max Eugene. geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff. United States: N. p., 2017. Web. doi:10.2172/1352403.
Light, Max Eugene. geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff. United States. doi:10.2172/1352403.
Light, Max Eugene. Thu . "geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff". United States. doi:10.2172/1352403. https://www.osti.gov/servlets/purl/1352403.
@article{osti_1352403,
title = {geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff},
author = {Light, Max Eugene},
abstractNote = {This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density ne(r), which will modify the wave propagation in the direction of the gradient rne(r).},
doi = {10.2172/1352403},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Apr 13 00:00:00 EDT 2017},
month = {Thu Apr 13 00:00:00 EDT 2017}
}

Technical Report:

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  • The geometric optics theory is applied to an inhomogeneous plasma in which the dielectric tensor is not necessarily Hermitian. A complex dispersion relation for a non-degenerate plasma is obtained as well as complex ray tracing and amplitude equations. From the amplitude equation is possible to identify and separate the focusing effects according to their effects on the plasma e.g., those ones due to cutoffs and resonances.
  • The paraxial WKB (pWKB) approximation, also called beam tracing method, has been employed in order to study the propagation of lower hybrid (LH) waves in a tokamak plasma. Analogous to the well-know ray tracing method, this approach reduces Maxwell's equations to a set of ordinary differential equations, while, in addition, retains the effects of the finite beam cross-section, and, thus, the effects of diffraction. A new code, LHBEAM (Lower Hybrid BEAM tracing), is presented, which solves the pWKB equations in tokamak geometry for arbitrary launching conditions and for analytic and experimental plasma equilibria. In addition, LHBEAM includes linear electron Landaumore » damping for the evaluation of the absorbed power density and the reconstruction of the wave electric field in both the physical and Fourier space. Illustrative LHBEAM calculations are presented along with a comparison with the ray tracing code GENRAY and the full wave solver TORIC-LH.« less
  • The theory of the propagation of small amplitude waves via the linearized Maxwell and kinetic equations leads to a large system of differential equations. A constructive procedure has been developed for the systematic reduction in order of the system. Mode coupling and mode conversion enter in a natural way. For the case of transverse waves propagating parallel to the magnetic field the analytic results are in excellent agreement with the results of a numerical solution. The formal theory of geometric optics in magnetized plasmas has been shown to require a reinterpretation of the ''dielectric tensor'' sigma(kappa,..omega..,r,t) which occurs in themore » theory. It has been demonstrated by a direct treatment of the linearized Vlasov equation and the Maxwell equations that sigma(kappa,..omega..,r,t) must be interpreted not merely as the dielectric constant of an infinite homogeneous plasma which everywhere has the properties that the real plasma displays at the point r,t in question, but that corrections first order in the small parameter wave length over scale length must be added. These change the transport equation for the amplitude of the field, and affect such issues as electron cyclotron absorption.« less