Speaker
Hugo Pereira Hugon
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4002.pdf
Ray tracing in weakly turbulent, randomly fluctuating media: A
quasilinear approach
H. Hugon, J. P. S. Bizarro, R. Jorge
Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa,
1049-001 Lisboa, Portugal
Ray propagation of electromagnetic and sound waves in turbulent media is important in a
wide range of research areas, which can vary from astronomy and free-space communications
to the scattering of rf waves in plasmas.
y
We describe the ray propagation in weakly tur-
600
bulent media using a quasilinear (QL) approach,
500
which relies on the Hamiltonian form of the ray
equations and makes use of a second-order expan- 400
sion (in the medium and ray fluctuations) of the dis- 300
persion relation and ray equations, in order to inte- 200
grate the ensemble-averaged ray and its root-mean- 100
square (rms) spreading. Due to the second-order x
terms, the averaged ray may exhibit a drift when -100
0 100 200 300 400 500
compared with the zero-order, unperturbed one.
Figure 1: Average ray trajectories and their
The QL formalism is validated against Monte rms spreadings from the QL formalism (red)
Carlo (MC) calculations and, when possible, veri- vs. a MC calculation using 100 rays (black)
fied using analytical predictions. For this, a single
random mode and a multimode isotropic turbulent spectrum (see Fig. 1) was used as practical
examples. The level of turbulence fluctuations and its maximum wavenumber are chosen to be
not too small, yet small enough such that the second order expansion and the geometrical optics
approximation remain valid.
Overall, the agreement between the QL and MC results is fair, particularly for the distance
travelled by the average ray, its perpendicular rms spread and the averages of the wave-vector
components. This approach comes as an efficient alternative to MC calculations and, while
similar to the so-called statistical ray tracing [1], it appears to be much easier to implement in
the case of more complex geometries or dispersion relations (as when tracing rays in tokamaks).
References
[1] R. Epstein and R. S. Craxton, Phys. Rev. A 33, 1892 (1986)
