Autonomous Cryogenic Sapphire Oscillators Employing Low Vibration Pulse-Tube Cryocoolers At Nmij

Two liquid-helium-cooled cryogenic sapphire-resonator oscillators (CSOs), have been modified to operate using cryo-refrigerators and low-vibration cryostats. The Allan deviation of the first CSO was evaluated to be better than 2x10(-15) for averaging times of 1 s to 30 000 s, which is better than that of the original liquid helium cooled CSO. The Allan deviation of the second CSO is better than 4x10(-15) from 1 s to 6 000 s averaging time.