INVERSE AC JOSEPHSON EFFECT FOR A FLUXON IN A LONG MODULATED JUNCTION

We analyze motion of a fluxon in a weakly damped ac-driven long Joseph son junction with a periodically modulated maximum Josephson current d ensity. We demonstrate both analytically and numerically that a pure a c bias current can drive the fluxon at a resonant mean velocity determ ined by the driving frequency and the spatial period of the modulation , provided that the drive amplitude exceeds a certain threshold value. In the range of strongly ''relativistic'' mean velocities, the agreem ent between results of a numerical solution of the effective (ODE) flu xon equation of motion and analytical results obtained by means of the harmonic-balance analysis is fairly good; morever, a preliminary PDE result tends to confirm the validity of the collective-coordinate (PDE -ODE) reduction. At nonrelativistic mean velocities, the basin of attr action, in the position-velocity space, for phase-locked solutions bec omes progressively smaller as the mean velocity is decreased.