WAVE RECTIFICATION IN PLASMA SHEATHS SURROUNDING ELECTRIC-FIELD ANTENNAS

Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-mu s time res olution, were made on several recent sounding rockets in the auroral i onosphere. It is found that Langmuir and whistler waves are partially rectified in the plasma sheaths surrounding the payload and the sphere s used as antennas. This sheath rectification occurs whenever the HF p otential across the sheath becomes of the same order as the electron t emperature or higher, for wave frequencies near or above the ion plasm a frequency. This rectification can introduce false low-frequency wave s into measurements of electric field spectra when strong high-frequen cy waves are present. Second harmonic signals are also generated, alth ough at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are lo w enough for the antenna coupling to the plasma to be resistive.