= Plasma wave
A <plasma wave> is a collective disturbance of charged particles and electromagnetic fields in a <plasma>. Restoring forces can involve charge separation, magnetic tension or <pressure>, producing different branches rather than one universal <wave> speed.
For a cold unmagnetized <electron> fluid with effectively stationary neutralizing <ions>, electrostatic density oscillations have <electron> <plasma> <frequency> $\omega_{pe}=\sqrt{n_e e^2/(\epsilon_0m_e)}$. Displacing <electrons> creates an <electric field> that pulls them back; inertia produces oscillation. Measuring that <frequency> therefore constrains <electron> density. Thermal motion, <magnetic fields> and collisions modify the dispersion and damping, and must be included when the cold-fluid assumptions fail.
Back to article page
