Main features of space rubidium atomic frequency standard for BeiDou satellites
Wuhan Institute of Physics and Mathematics (WIPM) has been developing the space rubidium atomic frequency standard (RAFS) for BeiDou navigation satellite system since the late of 1990's. Design of the RAFS aims to realize high stability, small size, long lifetime, high reliability and space environmental adaptability. The physics package was designed in SFT scheme. A slotted tube cavity with small size and TE011 resonant mode was used to construct the cavity-cell assembly, and an argon lamp with long lifetime was used as the pumping source. The microwave chain includes a 10MHz VCXO, a 5.3125MHz synthesizer, a ×9 RF multiplier and a ×76 SRD multiplier. Electronic circuits were designed by using analog circuitry to minimize the risk of element failure in space. The day stability of the space RAFS's developed for BeiDou regional system distributes within 2~5×10-14. To meet the needs of BeiDou global system, design of the RAFS has been improved further. A slotted tube cavity with larger size and better resonant mode was used, the argon lamp was substituted with a filtered xenon lamp, and the phase noise of microwave chain was depressed further. A prototype of new generation space RAFS was built recently. Preliminary test showed that the day stability of the prototype has reached 3×10-15.
Characteristics of a novel kind of miniaturized cavity-cell assembly for rubidium frequency standards
A novel kind of cavity-cell assembly for rubidium frequency standards has been developed. The assembly utilizes a new magnetron-type microwave cavity. The cavity is of small size, easily manufactured with high machining precision, and the cavity frequency can be easily adjusted. Either the integrated filter technique (IFT) or the separated filter technique (SFT) can be used in this cavity-cell assembly. The assembly has a high signal-to-noise ratio. The frequency stabilities of rubidium atomic frequency standards with this assembly are 4times10 -12/tau1/2 for IFT and 2.7times10-12/tau1/2 for SFT, and its temperature coefficient and light shift are very low
Geomagnetic micropulsations due to the motion of ocean waves
When sea waves move in the magnetic field of the earth, electric currents are generated in the water volume. These currents give rise to a small magnetic field which perturbs the earth's field. For plane trochoidal waves, this perturbing field decays exponentially with altitude and lies in a vertical plane which is oriented in the direction of wave propagation. The magnitude of the perturbing field also depends upon the magnitude and dip angle of the earth's field, and upon the height, wavelength, and propagation direction of the sea waves. For north-south waves, sea state 5, and an altitude of 100 feet, the perturbation is of the order of 0.1 gamma.