Abstract: Environmental stray magnetic fields and those generated by circuit components can cause frequency shifts in the transition spectral lines of CPT（Coherent Population Trapping） atomic clocks,thus affect their long-term frequency stability.To reduce the interference magnetic fields introduced by traditional electric heating temperature control devices,a dual-layer heating z-type structure was adopted.Simulation was conducted using finite element analysis software to compare the distribution of axial magnetic fields generated by traditional and novel heating elements in an atomic cell.Results indicated that the interference magnetic field intensity of the dual-layer z-type heating structure could be reduced to 0.05% of that of traditional heating elements,and magnetic field uniformity improved by over 1 700 times.Further adjustments of the currents in each layer of the dual-layer heating elements could reduce the interference magnetic field to less than 15 nT,and the magnetic field fluctuation range due to temperature adjustments was just 0.33 nT.Tests in a magnetically shielded environment showed that the actual results were consistent with the simulations,significantly enhancing the long-term frequency stability of the CPT atomic clock.

Key words: Atomic clock, Coherent Population Trapping(CPT), Magnetic field intensity, Electric heating, Frequency shift, Frequency stability