Plasma wave cutoff
= Plasma wave cutoff
{title2=$n^2\to0$}
A point on a <plasma> <wave> branch where the local <wavenumber> tends to zero at finite <frequency>. The mode may change between propagation and evanescence. For a finite <magnetized cold-plasma dielectric tensor>, candidate cutoffs satisfy $PRL=0$; special propagation angles require checking which factor belongs to the chosen branch.