Enhanced microwave absorption in warm plasma: Modified Appleton-Hartree equation

Abstract

Summary form only given. Thermal effects may be of high degree of importance on electromagnetic wave propagation in the ionosphere as well as in the emerging applications of stealth technology. A further development for the Appleton-Hartree theory may be made by extending the existing theory to include the plasma thermal effects. In this work, we present the derivation of the magneto-ionic dispersion equation and the corresponding index of refraction, propagation constant and reflection coefficients for characterizing wave propagation in warm plasma immersed a uniform magnetic field that could be self generated or externally applied. The obtained expressions extend the well known Appleton-Hartree, magneto-ionic formula of stationary cold plasma to the case of warm plasma. To demonstrate the effects of plasma temperature on wave propagation and attenuation, a numerical example of the developed theory has been given for typical parameters that may exist in stealth technology applications. Electron temperature range from cold plasma limit up to vTh ~ 0.05c, where vTh represents the electron thermal energy and c the speed of light, and a collisional plasma frequency ranges within (10-3,10+3), corresponding to the vTh range (0,0.05c). It is well known that in cold plasma one the two forward propagating modes is weakly attenuated while the other weakly amplified. By comparing the propagation constant obtained for warm plasma with that for the cold plasma complex propagation constant of the classical AppletonHartree theory, we observed that the weak damping of one mode in the cold plasma is absolutely enhanced by the thermal effect, while the second (which is weakly amplified in cold plasma) follows an anomalous behavior around resonant frequencies with enhanced attenuation and enhanced amplification regions. Also, we apply the modified theory on calculating EM - wave absorption rates from plasma near a metallic wall and found that the thermal effect enhances the wave absorption.