Short DescriptionGeneral Ray Tracing code for 3D Plasmas. Cyclotron Emission Spectra.
Date/Active Use1994 to present
AuthorsA.P. Smirnov and R.W. Harvey
Purpose/Function/Special FeaturesGENRAY is a general ray tracing code for the calculation of electromagnetic wave propagation and absorption in the geometrical optics approximation. It provides a solution of the ray tracing equations in general non-axisymmetric geometry, although work to date is with axisymmetric equilibria with added toroidal perturbations. Several alternative dispersion functions D are provided in order to ray trace for EC, LH, and ICRF waves. Current drive is calculated based on Maxwellian distribution functions. Results are coupled to the CQL3D code to provide input for calculation of the rf QL diffusion coefficients.
Many individual, specialized ray tracing codes have been developed in the plasma physics community for application in varous plasma geomentries and situations such as fusion energy tokamak, stellerator, or reversed field pinch plasmas, magnetoshperic plasmas, and interstellar and solar wind plasmas. The basic objective of the GENRAY code is to provide a well-tested, well-documented code applicable in all these situations. The code is constructed for general geometry and wave mode; introduction of specific geometries and modes is facilitated by a modular design for the code. The code is applicable for arbitrary magnetic field, with general flux surfaces. The magnetic field is specified by splines of tabulated values or as an arbitrary function of space. The modular features facilitate introduction of new dispersion relations. The integration of the ray equations is carried out using analytic forms or numerical differentiation for the derivatives of the dispersion relation.
Cylindrical coordinates are used, enabling simplifications for axisymmetric plasmas but permitting investigation of general geometry situations. In axisymmetric devices, the code treats flux surfaces as a function of root(toroidal flux), root(volume), or root(area), for generality and compatibility with other codes. Absorption and linear current drive is calculated, and ray parameters are output for use by ancillary codes.
Basic AlgorithmsIntegration of the ray equations is carried out using Runge-Kutta methods with fixed or adaptime step size, and methods are provided for conservation of the dispersion function along the trajectories.
For the ECE/EBW emission, methods developed in  are used. The radiation transfer equation is solved along WKB rays using a fully relativistic calculation of the emission and absorption from electron distributions which are limited only in being gyrotropic and toroidally symmetric, but may be otherwise arbitrary functions of the constants of motion. Using a radial array of electron distributions obtained from a bounce-averaged Fokker-Planck code such as CQL3D, we obtain the emission spectra.
Key ResultsThe code has been benchmarked against previous ray tracing codes for propagation of LH, FW, and EC waves in axisymmetric tokamak plasmas. Present work is focussed on non-axisymmtric effects on LH/FW propagation, and on EBWCD calculations.
EBWCD calculations [in conjunction with CQL3D] are provided for the MST and NSTX toroidal devices [4,5].