  We introduce a simple lattice model of superconducting vortices driven by
repulsive interactions through a random pinning potential. The model describes
the behavior at the scale of the London length lambda or larger. It
self-organizes to a critical state, characterized by a constant flux density
gradient, where the activity takes place in terms of avalanches spanning all
length scales up to the system size. We determine scaling relations as well as
four universal critical exponents for avalanche moments and durations: tau =
1.63 +/- 0.02, D = 2.7 +/- 0.1, z = 1.5 +/- 0.1, and tau_t = 2.13 +/- 0.14, for
the system driven at the boundary.
