Shock-front injection is an effective technique for controllably triggering electrons into a trapped phase for laser plasma acceleration. One common technique to achieve this fluid phenomenon is to impinge a thin blade on the plume of a supersonic nozzle. Naively, the common thought is that the shock produced by the blade is the bow shock from the first interaction; however, the density transition that is accessible by a laser transverse to the nozzle is produced by a rapid re-expansion of the high pressure region behind the initial bow shock. This imperfect re-expansion generates compression waves that could coalesce into shock-fronts as it interacts with the surrounding ambient gas which has consequences when interpreting the injection mechanism. Here the fluid dynamics of a supersonic nozzles impinged with a thin, flat object is explored along with their implications as electron beam injectors for laser plasma accelerators.
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