  We study the impact of spatial confinement on the dynamics of
three-dimensional excitation vortices with circular filaments. In a chemically
active medium we observe a decreased contraction of such scroll rings and even
expanding ones, despite of their positive filament tension. We propose a
kinematical model which takes into account the interaction of the scroll ring
with a confining Neumann boundary. The model reproduces all experimentally
observed regimes of ring evolution, and correctly predicts the results obtained
by numerical simulations of the underlying reaction-diffusion equations.

Pattern Formation and Solitons;Chemical Physics