Mach cone shocks in a two-dimensional Yukawa solid using a complex plasma

Mach cones were studied experimentally in a two-dimensional Yukawa solid consisting of charged micrometer particles suspended as a layer in a plasma. These cones were V-shaped shocks produced spontaneously by a supersonic particle moving below the main two-dimensional particle layer. The cones had a double structure. The first cone was compressional and particles moved forward, and it was followed by a second cone, which was rarefactional, where particles moved backward. Over the limited range of speed V attained by the supersonic particles in this experiment the angle mu. of the cone was found to obey the Mach cone rule sin mu=c/V where c is the medium's sound speed. The cones caused only elastic deformations in the crystal lattice, except in a narrow track behind the cone's vertex. The wings of the cones can be analyzed as linear shocks in two dimensions. Using spatially resolved measurements of the particle number density and velocity and applying the Hugoniot relations for shocks in two dimensions, we found that the pressure inside the first Mach cone was greater than in the undisturbed medium by a factor of 1.3-1.6. The cone angle was also used to measure the charge in this experiment.