A BAND THEORY OF HELICON PROPAGATION

The theory of helicon propagation in a periodic structure has been formulated. It assumes the plasma to be cold and collisionless, and introduces a periodic modulation of electron density or of external magnetic field. The dispersion equation is shown to break up into bands of allowed and forbidden propagation. Numerical results are presented for the density modulated case, and it is seen that the band gap is proportional to magnetic field and that the band edges move to higher frequency as the magnetic field is increased. Some comments on the possibility of constructing a tunable filter, based on helicon propagation, are included.