Observation of ponderomotively driven bow shock in a flowing underdense plasma*

High energy randomized laser beams can ponderomotively slow a flowing plasma. When the incoming flow is slowed from super-sonic to sub-sonic a shock is produced that propagates against the fluid velocity. Experiments on the OMEGA laser facility showed a density jump upstream of the laser focus consistent with a shock traveling upstream. A depression in density and fluid velocity were observed downstream of the laser focus again consistent with the ponderomotive slowing of the flowing plasma. Hydrodynamic simulations show these effects are only reproduced when the ponderomotive force of the laser is included. An upcoming Discovery Science experiment on the NIF will demonstrate bow shock formation in conditions relevant to ICF hohlraum laser entrance holes.