Creating and studying ion acoustic waves in ultracold neutral plasmas
  We excite ion acoustic waves in ultracold neutral plasmas by imprinting density modulations during plasma creation. Laser-induced fluorescence is used to observe the density and velocity perturbations created by the waves. The effect of expansion of the plasma on the evolution of the wave amplitude is described by treating the wave action as an adiabatic invariant. After accounting for this effect, we determine that the waves are weakly damped, but the damping is significantly faster than expected for Landau damping. 
T. C. Killian, P. McQuillen, T. M. O'Neil and J. Castro
physics.plasm-ph physics.atom-ph