  A Langmuir wave (LW) model is constructed whose equilibria are consistent
with stimulated Raman scatter optimization, with Hamiltonian dynamics and with
rotational invariance. Linear instability analysis includes terms to all orders
in wave amplitude and fluctuation wavenumber expansions, deltak. Resultant LW
modulational instability is nonstandard: as the LW amplitude increases,
unstable deltak range first expands and then shrinks to zero. Large amplitude
wave model dynamics requires hyper-diffraction terms if k LambdaD < 0.45, lest
artificially small length scales become unstable.
