We measure the decay of plasma waves to longer wavelengths, for both” standard”
Trivelpiece-Gould waves with v!!≫! v, and for the lower phase velocity “EAW” modes with
v!!~! v!. These are θ-symmetric standing modes on pure ion or pure electron plasma columns
with discrete wavenumbers!!= mz!!/Lp!. A large amplitude m!= 2! Trivelpiece-Gould wave
causes phase-locked exponential growth of the m!= 1! wave when they are near resonant, at
growth rates Γe∝!!" 2 n consistent with cold fluid theory. For larger detuning Δ≡ 2f1− f2 …