Damping Pram

In Physical, damping Pram , name of its discoverer, the Russian physicist Lev Davidovich Pram, corresponds to a transfer of energy between a electromagnetic Onde and electrons. This effect is similar to the Effet Čerenkov reverses.

This effect is used in particular in order to generate electric currents in plasmas reigning inside Tokamaks.

Interactions wave-particle

Landau damping is due to the energy exchange between a wave speed of phase

v_ {pH}

, and a particle in a plasma of which speed is roughly equal to

v_ {pH}

. The particles of which speed is slightly lower at the speed of phase of the wave will be accelerated by the electric field of the wave to reach the speed of phase. On the contrary, the particles of which speed is slightly higher at the speed of phase of the wave will be decelerated, yielding their energy to the wave.

In a collisionless plasma where speeds of the particles are distributed like a function Maxwellienne, the number of particles of which speed is slightly lower than the speed of phase of the wave is larger than the number of particles of which speed is slightly larger. Thus, it y' has more particles which gains in energy coming from the wave than of particles which yield some. Consequently, the wave yielding of energy, it is deadened.

Physical interpretation

A mathematical proof of Landau damping could be found in the references. One can however give a simple interpretation (although not strictly correct) which helps with the visualization of the phenomenon.

One can conceive the oscillations of plasma like waves in the sea, and the particles like surfers trying to hang up again itself with vaguenesses, the whole moving in the same direction. If the surfer moves at water surface at a speed slightly lower at the speed of the waves, it possibly will be ratrapé by the wave and thus will gain in energy. On the contrary, swimming surfer a more quickly than the speed of the waves will have to go up the peak of vagueness (thus yielding its energy to the prodit wave).

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