Reaction patterns in a blinking vortex flow*

We study the patterns formed by the excitable Belousov-Zhabotinsky reaction in a blinking vortex flow produced by magnetohydrodynamic forcing. Mixing in this flow is chaotic, as has been documented extensively in previous studies. The reaction is triggered by a silver wire, and the result is a pulse (``trigger wave'') that propagates through the system. We investigate the patterns formed by the propagating pulse and compare them with theories\footnote{T. Tel, A. de Moura, C. Grebogi and G. Karolyi, Phys. Rep. 413, 91 (2005).} that predict fractal patterns determined by the unstable manifolds of the flow. We also consider ``burn-like'' reaction fronts, and compare the results with previous experiments for patterns of oscillatory reactions in this flow.