  We have performed a study of several cesium oven designs. A comparison
between recirculating (or sticking-wall) or collimating (or reemitting-wall)
ovens is made in order to extract the most efficient design in terms of beam
brightness. Unfortunately, non-reproducible behaviors have been observed, and
the most often observed output flux is similar to the sticking-wall case, which
is the lowest theoretical value of the two cases, with a beam brightness close
to $10^{18}$ at.sr$^{-1}$.s$^{-1}$.cm$^{-2}$. The reason of this universally
observed behavior is unclear despite having tested several materials for the
collimating tube. Conclusion on possible improved design based on sticking of
cesium on several (un)cleaned surface is given.
