  The cloud of cold atoms produced by a Magneto-Optical Trap is known to
exhibit instabilities. We examine in this paper in which limits it could be
possible to realize an experimental trap similar to the configurations studied
theoretically, i.e. mainly traps where one direction is privileged. We study
the static behavior of an anisotropic trap, where anisotropy results
essentially from the use of two different laser frequencies for the arms of the
trap. Such a trap has very surprising behaviors, in particular the cloud
disappears for some laser frequencies, while it exists for smaller and larger
frequencies. A model is build to explain these behaviors. We show in particular
that, to reproduce the experimental observations, the model has to take into
account the cross saturation effects. Moreover, the couplings between the
different directions cannot be neglected.
