Well Peratt here was saying if there is 10^-4 ionization, EM is 10^7 times more dominant than gravity.
Even if there are neutral particles
(in this case 99%+ neutral with only 10^-4 ionized) in the plasma they get dragged along with.
Not shades of grey, this is developed empirically from Langmuir, Bostick, Alfven and the many other pioneering contributors.
Ofcourse, you are quite correct, different densities (dusty plasmas) and differing ionization levels will affect the result. Peratt in this instance has quoted one of the lowest ionization regions, being what we call "Neutral ionization region".
As ionization moves up, all the interesting morphology begins, spirals, double helix, etc.
http://www.plasma-universe.com/index...und_convection
Quote:
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In a partially ionized plasma, electromagnetic forces act on the non-ionized material indirectly through the viscosity between the ionized and non-ionized material.
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A good place to explore these scaling and ionization details is:
http://www.plasma-universe.com/Plasma_scaling