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Abstract
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The hydrody namic model is used to obtain a generalized pseudoforce equatio n throu gh which the
nonlinear response of periodicall y driven ion acoustic waves is studied in an electron-ion plasma
with isothermal and adiabatic ion fluids. The pseudo time series, corresponding to different driving
frequencies, indicates that nonlinearity effects appear more strongly for smaller frequ ency values.
The existence of extra harmo nic reso nances in the nonlinear amplitude spectrum is a clear indication of the interaction of an external force with harmonic compon ents of the nonlinear ion acoustic
waves. It is shown that many plasma parameters signifi cantly and differently affect the nonlinear
resonance spectrum of ion acoust ic excitatio ns. A heuristic but accurate mo del for the fo ldover
effect is used which quite satisfactorily predicts the bistabil ity of driven plasma oscillations. It is
remarked that the characteristic resonance peak of isothermal ion plasma oscillation s appears at
lower frequencies but is strong er compared to that of adiabatic ions. Comp arison of the exact
numerical results for fully nonlinear and approximate (weak ly nonlinear) models ind icates that a
weakly nonlinear model exaggerates the hysteresis and jump phenomeno n for higher values of the
external force amplitude.
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