We report experimental observation of periodic oscillation in a steady
state electron cyclotron resonance argon plasma that is not driven by
extra periodic forces. We interpret the oscillation according to the
predator-prey model, which is a nonlinear plasma-neutral coupling in t
he plasma production region. The oscillation is observed in a narrow p
lasma parameter window and is evidence for neutral density depletion i
n a high density plasma system. (C) 1996 American Institute of Physics
.