  An atomic rubidium beam formed in a 70 mm long two-dimensional
magneto-optical trap (2D MOT), directly loaded from a collimated Knudsen
source, is analyzed using laser-induced fluorescence. The longitudinal velocity
distribution, the transverse temperature and the flux of the atomic beam are
reported. The equivalent transverse reduced brightness of an ion beam with
similar properties as the atomic beam is calculated because the beam is
developed to be photoionized and applied in a focused ion beam. In a single
two-dimensional magneto-optical trapping step an equivalent transverse reduced
brightness of $(1.0\substack{+0.8-0.4})$ $\times 10^6$ A/(m$^2$ sr eV) was
achieved with a beam flux equivalent to $(0.6\substack{+0.3-0.2})$ nA. The
temperature of the beam is further reduced with an optical molasses after the
2D MOT. This increased the equivalent brightness to $(6\substack{+5-2})$$\times
10^6$ A/(m$^2$ sr eV). For currents below 10 pA, for which disorder-induced
heating can be suppressed, this number is also a good estimate of the ion beam
brightness that can be expected. Such an ion beam brightness would be a six
times improvement over the liquid metal ion source and could improve the
resolution in focused ion beam nanofabrication.
