Multiple Raman up-conversion of radiation from pre-existing Langmuir turbulence

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Abstract
The equilibrium states described by a damped and driven kinetic equation governing the evolution of the spectrum of radiation in a stationary Langmuir‐turbulent plasma are studied. Both Langmuir and transverse spectra are assumed to be one‐dimensional in wavenumber space. A source of radiation at the plasma frequency and a uniform rate of dissipation at the higher harmonics are assumed. The radiation is characterized by an effective temperature z, proportional to the Langmuir energy density and inversely proportional to the dissipation rate of the transverse waves. If zz. If z>1, photons scattered out of certain regions of phase space may return at a significant rate, and the spectrum is found to have a global maximum above the plasma frequency ωp. The location of this maximum is proportional to z1/3 ωp, which may be many times the plasma frequency. Applications to a laser‐plasma experiment and to the solar wind environment are discussed.