  The factors that influence the symmetry of an imploding detonation are
investigated experimentally and theoretically. Detonations in sub-atmospheric
acetylene-oxygen were initiated and made to converge in an apparatus that
followed that of Lee and Lee (Phys Fluids 8:2148-2152, 1965). The width of the
test section was controlled with a wave-shaping insert, which formed the test
section against the viewing window, creating an effectively two-dimensional
problem with a channel width comparable to the detonation cell size. The
convergence of the detonation was observed via self-luminous open-shutter
photography and high-speed videography. The resulting videos were analyzed to
quantify the wave speed, degree of asymmetry, and direction and magnitude of
the offset in the center of convergence. To determine the experimental
parameters that influence the symmetry of the imploding wave, the wave-shaping
insert was intentionally canted by 0.3{\deg}-0.6{\deg}, accentuating the
asymmetry of the imploding detonation. The experiment was modeled using a
Huygens construction wherein the detonation is treated as a collection of
wavelets, each assumed to propagate locally at a velocity determined by the
channel width. The results of the model reproduced the observed offsets in
detonation convergence from the center of the apparatus, confirming that
velocity deficits resulting from the narrow channel width control the observed
asymmetry.
