  Interferometric measurements with matter waves are established techniques for
sensitive gravimetry, rotation sensing, and measurement of surface
interactions, but compact interferometers will require techniques based on
trapped geometries. In a step towards the realization of matter wave
interferometers in toroidal geometries, we produce a large, smooth ring trap
for Bose-Einstein condensates using rapidly scanned time-averaged dipole
potentials. The trap potential is smoothed by using the atom distribution as
input to an optical intensity correction algorithm. Smooth rings with a
diameter up to 300 $\mu$m are demonstrated. We experimentally observe and
simulate the dispersion of condensed atoms in the resulting potential, with
good agreement serving as an indication of trap smoothness. Under time of
flight expansion we observe low energy excitations in the ring, which serves to
constrain the lower frequency limit of the scanned potential technique. The
resulting ring potential will have applications as a waveguide for atom
interferometry and studies of superfluidity.
