Two-parameter locus of boundary crisis: mind the gaps!

Boundary crisis is a mechanism for destroying a chaotic attractor when one parameter is varied. In a two-parameter setting the locus of boundary crisis is associated with curves of homo- or heteroclinic tangency bifurcations of saddle periodic orbits. It is known that the locus of boundary crisis contains many gaps, corresponding to channels (regions of positive measure) where a non-chaotic attractor persists. One side of such a subduction channel is a saddle-node bifurcation of a periodic orbit that marks the start of a periodic window in the chaotic regime; the other side of the channel is formed by a homo- or heteroclinic tangency bifurcation associated with this diffferent saddle periodic orbit. We present a two-parameter study of boundary crisis in the Ikeda map, which models the dynamics of energy levels in a laser ring cavity. We confirm the existence of many gaps on the boundary-crisis locus. However, the gaps correspond to subduction channels that can have a rather different structure compared to what is known in the literature.