Temperature dependence of pump coupling in two-plasmon decay instability of an electromagnetic wave in homogeneous fluid plasmas

Abstract

We have re-examined the pump-coupling term of the growth rate, in the fluid-Maxwell theory for the weak-damping limit of the two-plasmon decay instability of an electromagnetic wave (pump) in a homogeneous plasma. We found that the maximum pump coupling is obtained as (k0v0/4)(2TL/T−1) for electron temperatures T exceeding TL[≡(2/9)(1−4n/nc)(mc2)]. The well-known result for the pump coupling as k0v0/4 is only valid for T<TL. We found that the configuration of electron plasma waves is described by a lemniscate (an 8-shaped curve) for T>TL and by a hyperbola for T<TL. Thus, the pump coupling is reduced by electron heating and vanishes at the temperature equal to 2TL. The temperature-dependent pump coupling can occur even for a relatively cold plasma because the boundary temperature TL can be small if the electron density n is sufficiently close to the quarter critical (nc/4). Here, k0 is the pump wavenumber, v0 is the velocity amplitude of an electron oscillating under the pump electric field, nc(≡ω02m/4πe2) is the critical density, m is the electron particle mass, c is the speed of light in free space, ω0 is the pump angular frequency, and e is the electron particle charge.