Newsgroups: sci.physics.plasma
From: oliveria@hadron.engin.umich.edu (Roque Donizete de Oliveira)
Organization: University of Michigan Engineering, Ann Arbor
Subject: complex group velocity

I'm looking for recent references that discuss
the problem of whether or not complex group
velocity makes sense

d \omega dD/dk
Vg = --- = - ---------
dk dD/d\omega

I'm solving the plasma dispersion equation D(k,\omega,z) = 0
for parallel propagation (whistler waves, k parallel
to static magnetic field along the z-axis).
I'm solving it for the boundary value problem, i.e.,
complex wavenumber k and real frequency \omega.

As I solve D(k,\omega,z) = 0 for fixed \omega at several
axial positions, wave relections seems to be taking place
(as evidenced by a cusp in the real part of k and group
velocity becoming very small (and then Vg changes sign)).

I just want to know how to detect (numerically, not by visual
inspection of plots of k versus z) that wave reflection is taking
place. I thought monitoring the group velocity is the
conventional way of doing this. I just wondered about the
fact the Vg is complex and at some positions its imaginary
part is larger than the real part.

Thanks.

Roque
oliveria@engin.umich.edu