Landau Damping of Low- and High-Power Slow Electrostatic Waves

We have excited waves in a warm plasma and have observed strong absorption when ωk_∥3vₑ, in agreement with the predictions of linear Landau damping. At a certain critical power level, consistent with the power required to flatten the velocity distribution, the absorption disappears. Above this level we have obtained evidence for the appearance of an enhanced electron tail, in and above the energy range where Landau damping should occur.