Effect of pinning on nonlinear dynamics and dissipation of a trapped vortex driven by a strong surface current in a superconducting film.

We report numerical simulations of a trapped elastic vortex driven by a strong ac magnetic field $H(t)=H\sin\omega t$ parallel to the surface of a superconducting film. The power dissipated by the oscillating vortex driven by the ac Meissner current has been calculated by taking into account the vortex line tension, viscous drag and different pinning landscapes, including bulk, surface and cluster pinning. We show that the global surface resistance $\bar{R}_i(H)$ averaged over different statistical realizations of a random pinning potential exhibits a linear increase at small fields and levels off at higher fields. At high field amplitudes $R_i(H)$ was calculated, taking into account a nonlinear Larkin-Ovchinnikov (LO) viscous drag coefficient $\eta(v)$. Our numerical results show that at high fields $R_i(H)$ becomes a nonmonotonic function of $H$ which {\it decreases} with $H$ at higher frequencies. We also observed the jumpwise LO instability of fast perpendicular vortices in a film with weak pinning at small field amplitudes and frequencies.