Parametric decay instabilities in the HELIX helicon plasma source

Parametric decay of the electromagnetic helicon pump wave into two electrostatic waves, thought to be a lower hybrid wave and an ion acoustic wave, is observed. The parametric excitation of the electrostatic waves is strongest near the axis of the helicon source. The parametrically excited wave amplitudes can be as large as 8% of the pump wave amplitude. Thus, efficient coupling between the parametrically excited waves and plasma particles (ions and electrons) can lead to enhanced plasma densities, electron temperatures, and ion temperatures. A correlation between the lower hybrid wave and electron temperatures and a correlation between the ion acoustic wave and ion temperatures near the antenna are observed.