ON THE USE OF ATMOSPHERIC-PRESSURE PLASMAS AS ELECTROMAGNETIC REFLECTORS AND ABSORBERS

Tenuous plasmas in the earth's atmosphere from sea level to 100 km can be modeled as a cold collisional plasma. If an ionization process results in an electron density profile, such as an Epstein profile, that decreases from a maximum as a function of distance, then the plasma can either reflect or absorb electromagnetic waves, depending on the plasma characteristics. A high reflection coefficient requires a grazing angle of incidence, a low momentum-transfer collision rate, a high plasma density, and a short free-space-to-plasma transition relative to a wavelength. High absorption from VHF through X-band requires a high collision rate, a low plasma density, and a plasma transition of approximately one wavelength. Both extremes are discussed. Typical collision rates and plasma lifetimes at atmospheric pressure are quantified. The power required to sustain a plasma in air is high because of a short plasma lifetime, but a noble gas contained within a membrane has a longer plasma lifetime and a lower power requirement. Two means of ionization are discussed: high-energy electronbeam impact and UV photoionization of an organic vapor. © 1990 IEEE