Absorption of high frequency electromagnetic waves in a magnetoplasma

Measurements of strong absorption of high frequency (ω≃ωc, ω/2π=2.45 GHz electromagnetic waves in a plasma (ωp2/ω2=2.7) are reported. The absorption is almost complete; the transmitted power is less than 0.1% and the reflected power is less than 5%. Coincident with the onset of strong absorption is the appearance of microwave energy in the plasma in two frequency bands, and an increase in the electron temperature (from 6 to 10 eV). One frequency band is close to the plasma frequency (ωp/2π≃4 GHz); the second is a low frequency band below 2 GHz. These modes are identified as being of the Gould–Trivelpiece type. Wave amplitude, combined with transmitted and reflected power measurements, suggest that 95% or more of the incident energy may be converted into the low frequency modes which are trapped in the plasma and thus can be dissipated via resistive absorption.