Characteristics of oblique shock waves produced in an expanding laser plasma

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Abstract
Stationary oblique shock waves produced by a laser-produced plasma (carbon and lithium) expanding over a wedge and related phenomena have been investigated experimentally. Such a plasma is characterized as an ionization-frozen multicomponent flow which consists of a number of different charge-state groups with different flow velocities. Well-defined multiple shock fronts which are formed around a wedge are differentiated using a spectroheliographic method. Data obtained from an ion-charge collector and from spectroheliographs indicate that these shock fronts (with different inclinations) result from different flow components. The plasma behind the shock is predominantly recombining rather than ionizing. In addition, the innermost shock is found to be more like a transverse shock where the flow particles are transported along the shock plane. This is also evidenced by a large charged-particle cumulation (and collimation) which occurs when two such oblique shock waves are brought to intersect each other. The measured shock inclinations as a function of wedge angle indicate a considerable departure from a simple gasdynamic flow model. It is believed that the self-generated (reversed) magnetic field associated with the laser-produced-plasma shock greatly influences the shock behavior.