Plasma oscillation Totally Explained

Everything about Plasma Frequency totally explained

Plasma oscillations, also known as "Langmuir waves" (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals. The frequency only depends weakly on the wavelength. The quasiparticle resulting from the quantization of these oscillations is the plasmon. Langmuir waves were discovered by American physicists Irving Langmuir and Lewi Tonks in the 1920s. They are parallel in form to Jeans instability waves, which are caused by gravitational instabilities in a static medium.
In 2006, plasma physicists at the Universities of Texas and Michigan were able to photograph Langmuir waves, generated by a 30 TW laser pulse, for the first time.

Explanation

Consider a neutral plasma, consisting of a gas of positively charged ions and negatively charged electrons. If one displaces by a tiny amount all of the electrons with respect to the ions, the Coulomb force pulls back, acting as a restoring force.

'Cold' electrons

If the electrons are cold, it's possible to show that the charge density oscillates at the plasma frequency ť

omega_,

so the plasma waves can accelerate electrons that are moving with speed nearly equal to the phase velocity of the wave. This process often leads to a form of collisionless damping, called Landau damping. Consequently, the large-k portion in the dispersion relation is difficult to observe and seldom of consequence.
In a bounded plasma, fringing electric fields can result in propagation of plasma oscillations, even when the electrons are cold.
In a metal or semiconductor, the effect of the ions' periodic potential must be taken into account. This is usually done by using the electrons' effective mass in place of m.

Further Information

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