Nonresonant Parametric Decay of a Finite Extent Lower Hybrid Wave

The decay of lower hybrid waves into nonresonant quasimodes inside the lower hybrid resonance cone is observed. Sideband frequency shifts of up to 30 percent from the pump frequency occur. The low-frequency mode is identified as a nonresonant quasi-mode satisfying the approximate conditions ω/k‖ ≃ υe. The sideband wave-number and the sideband and quasi-mode growth rates were measured. The transition between ion-acoustic mode and quasi-mode decay spectra is observed as plasma density or pump frequency is varied.