We discuss the explosive instability caused by the nonlinear interaction of two positive energy waves and one negative energy wave and its stabilization by higher-order nonlinear effects.

An expanding or contracting non-neutral plasma without an external magnetic field is investigated. In certain situations the density and temperature rise to many times their initial values in a short time. followed by an equally sharp fall. The plasma shows no Landau damping.

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A study has been made of three-wave interaction and nonlinear wave-particle scattering for waves propagating parallel to the external magnetic field using quantum techniques. The three-wave interaction refers to longitudinal, transverse, and Alfvén or whistler modes. The waves taking part in the nonlinear wave-particle scattering are transverse, Alfvén, and whistlers. Kinetic equations containing these effects have been derived. It is established the three-wave interaction for Alfvén or whistler modes is impossible.