Instability of ion acoustic waves due to the return current driven by an electron heat flux is identified as a source of the ion-acoustic turbulence (IAT) in hot, inertial confinement fusion plasmas. Two mechanisms of anomalous absorption are studied, first due to enhanced electron collisionality on ion-acoustic fluctuations and second due to electromagnetic wave conversion into Langmuir waves at the critical density, which is enabled by IAT. An effective absorption coefficient is derived combining the two mechanisms with a stationary IAT spectrum derived from the theory of weak plasma turbulence. Estimates of the return current instability threshold and anomalous absorption are presented for hohlraum plasma in indirect drive fusion experiments. Anomalous absorption is anisotropic due to the angular anisotropy of the IAT spectrum and, according to our theory, can be remarkably effective near the critical density in high Z plasmas. Possible experiments which could identify IAT, and anomalous absorption mechanisms are discussed.
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Bychenkov et al. (2017) studied this question.