Two types of large-amplitude ion-acoustic fluctuations generated by the two-plasmon decay instability

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Abstract
An experimental survey of ion‐acoustic turbulence using ruby‐laser Thomson scattering in a CO2‐laser‐produced gas target plasma reveals two types of large‐amplitude ion fluctuations which arise from the action of the two plasmon decay (2ωp) instability. The first type is a direct result of the ponderomotive force generated by a pair of 2ωp decay waves driving ion waves at the difference wave vector. The second type is observed temporally delayed against the 2ωp instability and consists of a return current‐driven ion‐acoustic instability. The return current is a result of the electrostatic plasma potential generated during energetic electron emission by the 2ωp waves.