Electrostatic Surface Plasma Modes in Hot Planar Plasma Waveguide Structure

Field-matching technique and kinetic theory of plasma have been used to investigate the dispersion relation of the electrostatic surface plasma modes. We considered a configuration of two identical plasma slabs separated by a vacuum spacer with the rest of space being vacuum. In the limit
$k\to 0$
, where
$k$
is the propagation constant along the interface, the dispersion relation of surface plasma waves of hot and warm plasma slabs shows the emergence of asymmetric surface plasma modes with frequency starting from the electron plasma frequency
$\omega _{\mathrm{ pe}}$
and symmetric surface modes starting from zero frequency. As
$k$
increases, the frequencies of surface modes approach a common value, and the surface plasma modes become degenerate at a frequency above the cold plasma quasi-resonance frequency of a single plasma–vacuum interface
$\omega _{\mathrm{ sp}}=\omega _{\mathrm{ pe}}/\sqrt {2}$
. The two surface plasma modes of each branch of the dispersion relation are localized each near one of the two slab surfaces. By virtue of the finite slab widths, the two surface modes interact via the overlap of their evanescent fields to form asymmetric and symmetric pair of fields. The disagreement between the warm and hot plasma theories in the limit of large wave phase velocity compared with the thermal speed of electrons is due to the difference in their thermal dispersions. The surface plasma modes for hot plasma slabs are heavily Landau damped with negative frequency imaginary parts that overlap for small Debye lengths compared with the plasma width.