Why is the dielectric permittivity equated to "zero" in order to derive the (linear) dispersion relation for any excitable mode in plasmas?

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Federico Brivio

I am not sure what are you working about but I guess this could be of help::

http://farside.ph.utexas.edu/teaching/em/lectures/node100.html

P.K. Karmakar

Thanks a lot, Sir. It is useful. However, it remains yet to be well clarified why the plasma dielectric response function is equated to zero to arrive at the dispersion relation.

A few references may please be added.

Thanking you with regards,

PK Karmakar

Igor Goliney

Because of the fourh Maxwell equation div D = 0.

D = eps E, if eps = 0, E can be arbitrary.