Čerenkov-Like Radiation by Plasma Oscillations

A coupling mechanism is shown to exist between electrostatic oscillations along a plasma cylinder and transverse electromagnetic waves outside, resulting in radiation by phase oscillations. Plasma oscillations along the cylinder can be decomposed into traveling waves with plasma velocity $v_p=\frac{\omega }{k}$. The macroscopic appearance of such a traveling wave is the same as if a series of alternating positive and negative charged bunches move with the phase velocity of the wave. For long wavelengths, where the phase velocity exceeds the speed of light in the surrounding medium, radiation takes place, having a pattern as expected from Čerenkov radiation of the charged bunches moving with $v_p$. Since for plasma oscillations $\frac{\omega }{k}>c$ modes exist (Dawson and Oberman), this radiation can also take place in vacuum.