Influence of symmetry about the magnetic vector on the spectrum of light scattered by a magnetized plasma

The spectrum of light scattered by a plasma in a magnetic field is computed with real geometry effects included. When the scattering vector k is almost perpendicular to the magnetic field B, the spectrum consists of a sequence of peaks which are smeared unless 2kvesin phi <or= omega ce. Experimentally, scattered light is collected over a cone of k vectors and the spectrum which is observed consists of contributions from all the k's within this cone. Owing to symmetry about B, these composite distributions are strongly influenced by contributions from k's nearly perpendicular to B, and their modulation is much greater than that calculated for a single k vector on the edge of the cone. For a cone of a given angle, the deepest modulation occurs when its axis is perpendicular to B. Smearing due to misalignment of the cone axis is not serious until the perpendicular to B falls outside the cone. A general conclusion is that it is considerably easier in practice to meet the conditions required for the observation of magnetic modulation in a scattered light experiment than has been believed hitherto.