FORCES ACTING ON MAGNETOOPTICALLY TRAPPED ATOMS

We investigated how the size of ring-shaped clouds of cold, magneto-op tically trapped sodium atoms depends on the trapping parameters: magne tic-field gradient and laser intensity, detuning, and misalignment. Th e experiments were carried out in the low-density regime (N < 10(6) at oms), and the ring radius was shown to be independent of the number of trapped atoms. The results are explained with a simple model includin g a coordinate-dependent vortex force and the usual magneto-optical tr ap forces.