Three-dimensional saturation spectrum of the parametric decay instability


  • A. C. Das,

  • J. A. Fejer,

  • N. J. Martinic


The three-dimensional saturation spectrum of the parametric decay instability is obtained numerically, taking the true polarization of the pump field into account. In previous works the pump electric field was taken to be parallel to the inclined geomagnetic field, although that condition is only satisfied generally by an ordinary (pump) wave if its frequency ω is equal to the plasma frequency ωp or if its propagation vector is perpendicular to the magnetic field. The spectrum obtained numerically for ω0 = 1.04 ωp deviates strongly from axial symmetry about the geomagnetic field, especially for the large angle of inclination existing at Tromsø. The results obtained will therefore be important for the interpretation of the saturation spectrum observed with the aid of the EISCAT 933-MHz UHF radar (which detects Langmuir waves for which ω0 ∼ 1.04 ωp) during ionospheric modification experiments near Tromsø.