Unified Theory of Stimulated Raman Scattering and Two-Plasmon Decay in Inhomogeneous Plasmas: High Frequency Hybrid Instability

The theories of stimulated Raman scattering (SRS) and two-plasmon decay (2{omega}{sub {ital pe}}) in inhomogeneous plasmas have been unified by adopting a powerful new variational approach. We call this technique the minimum pump strength principle (MPSP), and the unified process, the high frequency hybrid instability (HFHI). The growth rate and frequency shift of the most unstable mode of HFHI are shown to match smoothly onto the two known limiting cases: 2{omega}{sub {ital pe}} at large {ital k}, and SRS backscattering as {ital k} goes to zero. The effectiveness of this method has allowed the generalization of the density inhomogeneity treated from a constant gradient to any positive-integer power law. Potential experimental signatures of HFHI modes are described. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.