  The medium-long term frequency stability of the integrating sphere cold atom
clock was improved.During the clock operation, Rb atoms were cooled and
manipulated using cooling light diffusely reflected by the inner surface of a
microwave cavity in the clock. This light heated the cavity and caused a
frequency drift from the resonant frequency of the cavity. Power fluctuations
of the cooling light led to atomic density variations in the cavity's central
area, which increased the clock frequency instability through a cavity pulling
effect. We overcame these limitations with appropriate solutions. A frequency
stability of 3.5E-15 was achieved when the integrating time ? increased to 2E4
s.
