Three-dimensional structure of Mach cones in monolayer complex plasma
  Structure of Mach cones in a crystalline complex plasma has been studied experimentally using an intensity sensitive imaging, which resolved particle motion in three dimensions. This revealed a previously unknown out-of-plane cone structure, which appeared due to excitation of the vertical wave mode. The complex plasma consisted of micron sized particles forming a monolayer in a plasma sheath of a gas discharge. Fast particles, spontaneously moving under the monolayer, created Mach cones with multiple structures. The in-plane cone structure was due to compressional and shear lattice waves. 
L. Couedel, D. Samsonov, C. Durniak, S. Zhdanov, H. M. Thomas, G. E.   Morfill, and C. Arnas
physics.plasm-ph