BNM-SYRTE fountains: Recent results

This paper describes several recent improvements of the BNM-SYRTE fountain ensemble. A new method for controlling the cold collision shift with improved accuracy has been proposed and demonstrated. A thorough investigation of some cold collision properties of
¹³³
Cs is presented, including the observation of molecular Feshbach resonances. Finally, a new microwave synthesis scheme based on a fully operational cryogenic oscillator is presented. With this, a fractional frequency instability below 2 times 10
^-14
tau
^-frac12
is obtained routinely