Longitudinal Waves Excited in an Inhomogeneous Magnetized Plasma Slab

Excitation of short wavelength longitudinal oscillations in a plasma slab is considered for frequencies near the second harmonic of the electron cyclotron frequency. For the uniform plasma slab a long and short wavelength plasma oscillation coupled at the boundary and the relative amplitudes are governed by the boundary conditions. In the nonuniform plasma slab these two fields are continuously coupled within the slab as well as at the boundaries. When the boundaries are removed, these fields are coupled by the density gradient and the rapidly varying field is of amplitude λ2/L2 less than the long wavelength field where λ is the wavelength and L is the scale size. The slab plasma exhibits a series of resonances and antiresonances as a function of field B when B> mω/2e and shows an antiresonance for an excitation frequency slightly greater than the second harmonic. An experiment verified this predicted antiresonance.