抄録
On the basis of the W.K.B. method, it is shown that an inverse triangle density cavity can trap a pair of temporally growing, oppositely propagating electron Langmuir waves; these are parametrically coupled through a combined action of a density gradient inside the cavity and a high-frequency pump electric field which is uniform outside the cavity. The threshold value of the pump intensity for this decay instability is presented as a monotonously increasing function of the scale size of the trapping regions, the mode number, the Debye length, and the minimum threshold above which the decay instability of the convective-type sets in. Consideration of the electron ponderomotive force created by the intense pump field which is non-uniform inside the density cavity leads to a decrease of the density gradient, resulting in an appearance of the upper threshold above which the trapped waves are damped.
