Interaction of two-dimensional plasma crystals with upstream charged   particles
  Two-dimensional plasma crystals are characterized by a strong up-and-down asymmetry not only due to gravity but also due to the presence of plasma flow at the location of particles. We study for the first time the interaction of a single-layer plasma crystal with charged extra particles located above it (upstream of the flow of ions). Upstream extra particles tend to move between the rows of particles in the crystal, accelerate to supersonic speeds, and excite attraction-dominated Mach cones and wakes in the crystal. 
C.-R. Du, V. Nosenko, S. Zhdanov, H. M. Thomas, and G. E. Morfill
physics.plasm-ph cond-mat.soft