  Magneto-optical traps (MOTs) are widely used for laser cooling of atoms. We
have developed a high-flux compact cold-atom source based on a pyramid MOT with
a unique adjustable aperture that is highly suitable for portable quantum
technology devices, including space-based experiments. The adjustability
enabled an investigation into the previously unexplored impact of aperture size
on the atomic flux, and optimisation of the aperture size allowed us to
demonstrate a higher flux than any reported cold-atom sources that use a
pyramid, LVIS, 3D-MOT or grating MOT. We achieved 2.0(1)x10^10 atoms/s of 87-Rb
with a mean velocity of 32(1)m/s, FWHM of 27.6(9)m/s and divergence of
58(3)mrad. Halving the total optical power to 195mW caused only a 26% reduction
of the flux, and a 33% decrease in mean velocity. Methods to further decrease
the velocity as required have been identified. The low power consumption and
small size make this design suitable for a wide range of cold-atom
technologies.
