Abstract
The Space Active Hydrogen-Maser (SAHM) can be used for the Space Very Long Baseline Interferometry Project to improve the resolution of the space astronomical telescope. The standard frequency signals provided by the SAHM have their stability dependent on the flux of effective H atoms. Therefore, a nickel (Ni) tube, one end closed, has been designed in this paper for the SAHM as a hydrogen (H2) purification and flux control device. Mechanisms of the H2 purification and flux control by a Ni tube were studied. H2 flux and ΔU, as a function of an input current, are given by experimental analyses. The diffusion activation energy of atomic H is much less than that of other atoms under the same conditions in Ni. The H atoms reversibly diffuse in Ni, and their diffusion speed has a high response to temperature. Experimental research shows that when the temperature of the tube was changed (from 27 to 700 °C), by an input heating electrical current (from 0 to 3.5 A), the H2 flux varied from 0 to 9.18 × 10−10 mol/s and no change in the phase structure of Ni. The data of flux should be useful for the frequency stability performance research of the SAHM. In addition, no phase change of the material indicates a stable performance of the tube for H-purifying and flux controlling. Finally, the above advantages make it a promising candidate for the reliability of the SAHM.
Highlights
The atomic frequency standard is the most accurate timing instrument that can be realized at present
The following conclusions are obtained by experiments of transmission electron microscope (TEM), temperature-changed XRD, and H2 flux measurement by the sensor in the circuit: (1) The Ni tube is single-phase polycrystalline
(3) The H2 flux of the Ni tube output has been given by the Pirani circuit
Summary
The atomic frequency standard is the most accurate timing instrument that can be realized at present. Hydrogen-masers, with the frequency stability of 10−15–10−16/day, are called the heart of satellite for providing the satellite navigation system with standard time and frequency signals. They have an advantage of both having a good medium and long-term frequency stability performance, which gives them a priority in the field of precise astronomical observation application, such as the Very Long Baseline Interferometry (VLBI) and Square Kilometer Array (SKA).. A microwave signal generated by the atomic hyperfine transition of ground state H, from energy level F = 1, mF = 0 to F = 0, mF = 0, is used as the reference for locking the voltage-controlled crystal oscillator to realize the stable output signals of the instrument.. Collision with unexpected particles, such as the impurity gases, will change the H energy levels, reduce the number of effective H atoms, and limit the stability performance via the frequency expanding and/or shift of the transitional signal. H2 purity and vacuum are required
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