Parametrical Quasi-resonant Amplification of Alfven Waves in Heat-Releasing Isentropically Unstable Media

Abstract

Three-wave interactions of the powerful magnetoacoustic wave with the Alfvén waves in heat-releasing ionized media are considered. The system describing the parametrical decay of the acoustic wave is obtained. The solution of the obtained system is found analytically for long-wave and weak nonlinearity approximations. The obtained solutions for the Alfvén waves strongly depend on the frequency detuning ∆ω. When ∆ω equals zero, the amplification of Alfvén waves is resonant, non-threshold and bi-exponential. With frequency detuning increase, the parametrical amplification of Alfvén waves becomes slower; further on, modulation is observed before bi-exponential amplification; and, finally, there is only Alfvén wave modulation. The cause of the modulation, which is observed before the amplification, is the existence of a threshold for amplitude. Conditions of the Alfvén wave amplification caused by the quasi-resonant parametrical energy transfer from unstable magnetoacoustic waves are obtained.