Microwave-Vacuum Integrated Cavity with a Low Temperature Sensitivity for Cs Fountain Clocks

A low temperature-sensitive microwave-vacuum integrated cavity (MVIC) for Ramsey interrogation in Cs fountain clocks is proposed and experimentally prepared. This cavity is a typical TE011 cylindrical microwave resonator (CMR), which is made of a titanium (Ti) tube with two oxygen-free copper (OFC) end caps. The quality factor Q of cavity is improved by thin layers of copper and gold coating on the inner surface of the tube. The cavity resonance frequency (RF) changes are compensated thanks to the different thermal expansion of the different parts. Each coupling hole is sealed with a ceramic window first and then covered by a rectangular waveguide. Thus, the MVIC itself can be functioned both as the microwave resonator and a part of the vacuum chamber of the clock physical package. In contrast to the design with a cavity installed inside a vacuum chamber, the physical package with this MVIC is more compact, and more convenient for assembling. Additionally, the RF of the MVIC can be finally tuned after vacuum baking. The design and preparation processes of this Cs MVIC are introduced. And the results show that, for this prepared Cs MVIC, the sensitivity of its RF to the temperature variation is measured to be -48.1 kHz/℃, 3.2 times superior to a traditional OFC cavity with the same sizes.