Laser-cooled Rb fountain clocks

We demonstrate a prototype of a laser-cooled /sup 87/Rb fountain clock and report a preliminary measurement of the frequency shift due to cold collisions. We find the shift to be much smaller than that in a laser-cooled Cs clock. We have recently demonstrated a juggling atomic fountain to study cold collisions. We discuss the importance of juggling for future fountain clocks and the problems and potential solutions.