  We prove that all atoroidal automorphisms of $Out(F_N)$ act on the space of
projectivized geodesic currents with generalized north-south dynamics. As an
application, we produce new examples of non virtually cyclic, free and purely
atoroidal subgroups of $Out(F_N)$ such that the corresponding free group
extension is hyperbolic. Moreover, these subgroups are not necessarily convex
cocompact.
