Hot spot growth in plastic-bonded explosives (PBX) seen with high time and space resolution

One of the most fundamental processes in the shock-to-detonation or shock-to-deflagration transitions in PBX is hot spot growth. This can be quite complicated because the hot spot is a thermal explosion that produces a blast of hot material with a huge temperature gradient (10⁹K/m). Previously we developed a method to watch hot spots in real time by fabricating a thin wafer of PBX (HMX + binder) about one crystal thick and embedding the wafer in a transparent polymer. After shocking the wafer with a laser-launched flyer plate, we could observe every crystal in the PBX and watch hot spots with a nanosecond camera with 2-3 μm resolution via their intense visible thermal emission. Determining growth mechanisms was difficult because a complex hot spot ensemble was produced consisting of myriad subcritical and critical hot spots. Now we have shot our usual 500 μm diameter flyer plate through a small hole to produce a flyer plate to create a single hot spot as small as a single grain (~30 μm). With hyperspectral imaging we can measure temperature field so we can determine growth rates within a known temperature gradient. We can engineer the small holes to produce two or more hot spots a known distance apart. Of particular interest would be experiments on inhomogeneous explosives where we create an HMX hot spot adjacent to a metal or metal/oxidizer composite particle.