FLUXON-DENSITY WAVES IN A MODULATED JOSEPHSON RING

Collective excitations in a fluxon chain placed in a periodically modu lated Josephson junction are studied analytically and numerically. In order to eliminate fluxon collisions with boundaries, we consider a Jo sephson ring (annular Josephson junction). Due to the interaction of t he fluxons with periodically placed obstacles, we predict that linear deformation modes of the fluxon chain should bring about resonances wh ich can be observed experimentally. The linear analysis is compared wi th numerical simulations, and good agreement is found in an appropriat e parameter range. In the ''relativistic'' limit, the numerical simula tions reveal a dynamical mode which is characterized by a strongly non linear interaction between the moving fluxons in the chain. A qualitat ive explanation of this regime is suggested by an extrapolation of the linear behavior.