We describe experiments which throw light on the physics of high-Mach-number electrostatic shocks. A planar carbon target is irradiated with an 18-nsec laser pulse at a wavelength of 1.05 μm with an energy of 100–200 J. Carbon plasma ablates supersonically from the solid target at a velocity of 6×${10}^7$ cm ${\sec }^{\mathrm{-}1}$. A spherical carbon obstacle is placed in the ablating plasma at a distance of around 1 mm from the primary target where the density is ${10}^{18}$ electrons ${\mathrm{cm}}^{\mathrm{-}3}$. The density structure of the plasma is probed by interferometry and schlieren photography, and shows a density jump which can be interpreted as a bow shock in a plasma flowing with a Mach number of around 2.2. Measurements of magnetic field imply a plasma β (8πnkT/$B^2$) in excess of 100. The shock thickness is occasionally very thin (about 10 μm), but more usually 50 μm. In either case the shock thickness is much smaller than the electron and ion Coulomb mean free paths.

• Received 26 February 1988

DOI:https://doi.org/10.1103/PhysRevA.38.1363