Abstract
The nonlinear saturation of low-power-threshold two-upper-hybrid (UH)-plasmon parametric decay instability (PDI) of an extraordinary pump wave-excited in the presence of a nonmonotonous density profile is analyzed in detail. It is shown that the primary absolute PDI enhancing the UH wave fluctuations from the thermal noise level, which was analyzed in linear approximation in Popov and Gusakov (2015 Plasma Phys. Control. Fusion 57 025022), is saturated due to a secondary low-threshold decay of the daughter UH wave. The secondary decay leads to excitation of the secondary UH wave, downshifted in frequency and also trapped in the vicinity of the local maximum of the density profile, and the ion Bernstein wave. A set of equations describing the primary and secondary decays and accounting for the finite pump-beam width is derived and solved numerically. The results of numerical modeling are shown to be in agreement with an analytical estimation of the growth rates of both the primary and secondary parametric decays and of the saturation level. The anomalous absorption of the pump wave due to the two plasmon PDI is estimated at a level of 6% for the plasma density profile considered in the paper.
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