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The propagation for relativistically intense and broad spectrum EM
waves in magnetized plasmas is considered. A general kinetic
equation for the photon spectral function is derived and used to
obtain a set of hydrodynamical equations for the particular case
of helicon waves. Numerical calculations for the $1-D$ set of
equations with a Gaussian distribution function at $t=0$ shows
that the profile of density changes its shape in the course of
time and forms a discontinuity.
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