Parametrical Quasi-resonant Amplification of Alfven Waves in Heat-Releasing Isentropically Unstable Media
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.
This work was partially supported by the Ministry of Education and Science of Russia, project 3.1158.2017, by RFBR under grants 16-41-630591 r_a, 17-42-630224 r_a.