  Continuous plasma coherent emission is maintained by repetitive Langmuir
collapse driven by the nonlinear evolution of a strong electron two-stream
instability. The Langmuir waves are modulated by solitary waves in the linear
stage, and by electrostatic whistler waves in the nonlinear stage. Modulational
instability leads to Langmuir collapse and electron heating that fills in
cavitons. The high pressure is released via excitation of a short wavelength
ion acoustic mode that is damped by electrons and that re-excites small-scale
Langmuir waves---this process closes a feedback loop that maintains the
continuous coherent emission.
