Physics of Systematic Frequency Variations in Hydrogen Masers

The frequency stability of hydrogen masers for intervals longer than 10000 seconds is limited at present by systematic processes. We discuss the physics of frequency-determining mechanisms internal to the maser that are susceptible to systematic variations, and the connections between these internal mechanisms and external environmental factors. Based upon estimates of the magnitudes of systematic effects, we find that the primary internal mechanisms currently limiting long-term maser frequency stability are cavity pulling, at the level of parts in 10'5 per day, and wall shift variations, at the level of parts in 10 to the 16th power to parts in 10 to the 15th power per day. We discuss strategies for reducing systematic frequency variations. See also ADA239372. Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd) held in Vienna, VA on 4-6 Dec 1990. Published in the Annual Precise Time and time Internval Applications and Planning Meeting Proceedings, p453-464, Dec 1990.