Propagation of a Coherent Ion Acoustic Wave through Ion Wave Turbulence

A coherent test wave is allowed to propagate through a stationary and spatially evolving ion wave turbulence which is realized in an unmagnetized argon positive column. It is shown that the observed nonlinear saturation and subsequent damping of the test wave can be well described by an analytic expression based on the theory of perturbed ion orbits, i.e., by an effective increase of ion temperature, provided the initial amplitude of the test wave is less than a threshold value \(\tilde{n}_{k}^{*}(0)\). When the initial amplitude exceeds \(\tilde{n}_{k}^{*}(0)\), generation of subharmonic wave is observed. It is also found that contraction of the wavelength occurs when the test wave with an initial value less than \(\tilde{n}_{k}^{*}(0)\) propagates from a quiescent region to the turbulent region. These phenomena are considered as due to higher-order nonlinear effects.