Experimental arrangement for the Mach reflection experiment. Two opposing laser-heated hohlraums are used to ablate aluminum pushers that in turn drive counter-propagating shocks into a resorcinol-formaldehyde foam experimental package. The shock positions are recorded by x-ray backlighting radiography, using an area backlighting source and time-gated x-ray camera. The “Dante” x-ray diode array is used to monitor the hohlraum temperature.
The experimental package for the Mach reflection experiment, in which the incident , reflected , and Mach shocks are shown schematically and (bottom) typical experimental data. Dimensions are in microns.
Experimental images (obtained using a 4.75 keV x-ray backlighting source) showing formation of the Mach stem as a function of time. Dimensions are in microns. Note the changes of offset on the left-hand axis, which were chosen to centralize approximately the radially propagating Mach stem in each image.
(Top) Experimental data from the Mach stem experiment at , in which the incident shock , reflected shock , Mach stem , and slip surface discontinuity may all be identified. (Bottom) Notation for analysis of the experimental data. The angles and are defined by the tangent to the incident shock front at the position of the triple point . is the length of the Mach stem. The angle is the deviation from planarity of the Mach stem at the triple point.
PETRA simulation (at ) of the Mach stem experiment showing material interfaces and density distribution and synthetic 4.75 keV radiograph. Dimensions are in microns.
PETRA simulation (at ) of the Mach stem experiment showing temperature and velocity distribution. Note the temperature difference between the incident and Mach shocks, the velocity shear at the slip discontinuity (evident in the axial component of velocity), and the jetting at the symmetry plane (evident in the radial component of velocity, just inside the Mach shock). Dimensions are in microns.
Synthetic radiographs from PETRA simulation of the Mach reflection experiment. The Mach stem and slip discontinuity are evident at 10 ns and later, and the jetting phenomenon at the plane of symmetry is evident at 13 ns. Dimensions are in microns. Note the changes of offset on the left-hand axis, which were chosen to centralize approximately the radially propagating Mach stem in each image.
Location of shock positions in the experiment (black), and the PETRA (red) and RAGE (blue) synthetic radiographs. The shocks are identified by using the Canny edge-detection algorithm. In the case of the PETRA simulations, the data have been offset by a maximum of (compare with Fig. 9, which shows absolute positions) to aid comparison of shape. The amplitude of noise in the experimental data is dependent on the degree of spatial smoothing employed in the edge-detection process, although this does not affect the shape of the detected shock front.
Radial position of the Mach shock at the plane of symmetry in experiment and simulation.
Observed Mach stem length, , and mean angle of incidence, , of the incoming shock at the position of the triple point, for the experimental data and the PETRA and RAGE simulations.
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