Landau Damping - Wave-particle Interactions

Wave-particle Interactions

Landau damping occurs due to the energy exchange between a wave with phase velocity and particles in the plasma with velocity approximately equal to, which can interact strongly with the wave. Those particles having velocities slightly less than will be accelerated by the wave electric field to move with the wave phase velocity, while those particles with velocities slightly greater than will be decelerated by the wave electric field, losing energy to the wave.

In a collisionless plasma the particle velocities are often taken to be approximately a Maxwellian distribution function. If the slope of the function is negative, the number of particles with velocities slightly less than the wave phase velocity is greater than the number of particles with velocities slightly greater. Hence, there are more particles gaining energy from the wave than losing to the wave, which leads to wave damping. If, however, the slope of the function is positive, the number of particles with velocities slightly less than the wave phase velocity is smaller than the number of particles with velocities slightly greater. Hence, there are more particles losing energy to the wave than gaining from the wave, which leads to a resultant increase in the wave energy.