Rings on strings in excitable media

TL;DR

This paper investigates how threading vortex strings through coaxial vortex rings in the FitzHugh-Nagumo excitable medium alters their dynamics, preventing annihilation, enabling overtaking, and reversing motion through indirect interactions.

Contribution

It introduces the novel concept that vortex string threading significantly changes vortex ring interactions in excitable media, revealing new behaviors and interaction mechanisms.

Findings

Threading prevents ring annihilation in head-on collisions.

Threading enables generic ring overtaking.

Threading can reverse the direction of vortex ring motion.

Abstract

We study the dynamics and interaction of coaxial vortex rings in the FitzHugh-Nagumo excitable medium. We find that threading vortex rings with a vortex string results in significant qualitative differences in their evolution and interaction. In particular, threading prevents the annihilation of rings in a head-on collision, allows generic ring overtaking, and can even reverse the direction of motion of a ring. We identify that an important mechanism for producing this new behaviour is that threaded vortex rings interact indirectly via induced twisting of the threading vortex string.