SCATTERING OF ELECTROMAGNETIC-WAVES BY COUNTER-ROTATING VORTEX STREETS IN PLASMAS

The scattering of electromagnetic waves from counter-rotating vortex s treets associated with nonlinear convective cells in uniform plasmas h as been considered. The vortex street solution of the Navier-Stokes or the Hasegawa-Mima (and of the ''sinh-Poisson'') equation is adopted a s a scatterer. Assuming arbitrary polarization and profile function fo r the incident electromagnetic field, a compact expression for the sca ttering cross section has been obtained. Specific results for the diff erential cross section are obtained for the case in which the incident beam has a Gaussian profile and propagates as an ordinary mode. The r esults show that when the characteristic wavelength of the vortex stre et (lambda(upsilon) = 2 pi/a) is larger than that of the incident elec tromagnetic wave (lambda(i) = 2 pi/k(i)), the differential cross secti on d sigma/d Omega has a very well-defined angular periodicity; in fac t, it is a collection of Gaussians varying as exp[-f(k(i)w)(2)], where w is the waist and f is a function expressing a kind of ''Bragg condi tion.'' On the other hand, for lambda(i)>lambda(upsilon) the incident electromagnetic beam is unable to distinguish the periodic structure o f the vortex street. The effects of the vortex street as well as the i ncident beam parameters on the scattering cross section are examined. (C) 1996 American Institute of Physics.