Simulation and Application of Multi-section Coil for C Field Used in Space Passive Hydrogen Maser

Space passive hydrogen maser (SPHM) has the advantages of high frequency stability and low frequency drift. It has been widely used in the navigation systems and frequency calibration. The quantum transition of hydrogen atoms and its signal detection are realized in the cavity-blub assemble of the spaceborne hydrogen atomic clock. Atomic transition signal amplitude of SPHM directly determines the system signal to noise ratio, and thus affects system performance, which makes cavity-bulb assemble one of the most important parts of SPHM.Straight solenoid is widely used in cavity-bulb assemble of SPHM to generate the constant magnetic field (C field) for atomic transition. Due to structural restriction of physical package, there is improvement potential for homogeneity of C field. This paper discusses the feasibility of using multi-section coil for generating the C field in SPHM. Firstly, the magnetic field generated by multi-section coils is theoretically analyzed and calculated. Then simulation and optimization of the parameters of the multi-section coil is carried out by ANSYS electromagnetic simulation software, the length of each section, their quantity, spacing, turns, diameter and total length. Design of multi-section coil with better homogeneity for the C field can be given by the simulation software. Inhomogeneity of about 1% of the C field is realized comparing to about 10% of the straight solenoid.According to the optimization results, the experimental nine-section coil was manufactured. The testing and comparison of atomic transition signal gain with diffident C field were carried out. Meanwhile, the closed-loop test was done in combination with the electronic package, and frequency stability of SPHM was measured and compared. Experimental results show that atomic transition signal gain can be effectively increased with the use of multi-section coil, and frequency stability is better in the middle and short-term stability (1-1 000 s), which is beneficial to further performance improvement of SPHM.