Saturation of Low-Threshold Two-Plasmon Parametric Instability of an Extraordinary Wave in an Inhomogeneous Plasma

Saturation of low-threshold parametric decay instability of an electron cyclotron wave of extraordinary polarization is analyzed; the development of this instability near a local maximum of the plasma density profile gives rise to two upper hybrid (UH) plasmons at frequencies close to the half of the pump wave frequency. As a saturation mechanism of this instability, a cascade decay of daughter UH waves is used, which leads to the excitation of secondary UH and lower hybrid (LH) waves that are also radially localized in the vicinity of a local maximum and minimum of the plasma density profile, respectively.