Propagation at any angle to the imposed magnetic field

Abstract

For propagation at any angle to the imposed magnetic field, the direction of group propagation in general differs from the direction of phase propagation as described in Chapter 6. It is convenient to begin by supposing that the direction of phase propagation is specified. We are then considering an infinite homogeneous plasma subject to a steady uniform magnetic field, and waves are being launched from an infinite antenna plane whose normal makes an angle θ p with the direction of the imposed magnetic field. If the wave in the plasma is to be described by means of a single exponential wave function, the antenna must have a specific elliptic polarization (Section 5.5). There are two such elliptic polarizations, corresponding to the two characteristic waves, and these waves propagate with different phase velocities. For an antenna with finite aperture dimensions, the relation between the beam direction and the normal to the aperture plane is as illustrated in Figure 6.3. Moreover, for a given orientation of the aperture plane, the beams for the two characteristic waves in general point in different directions. Furthermore, if the antenna is pulsed, wave packets travel along the two beams with different velocities.