Fig. 1. Die cut drawing of a transportable rubidium fountain atomic clock

Fig. 2. Residual magnetic field distribution inside the magnetic shield after demagnetization

Fig. 3. Magnetic field coil. (a) C－field coil and its compensation coil; (b) state selective compensation coil

Fig. 4. Theoretical calculation of magnetic fields for C-field unicoil and C-field unicoil with compensation coils

Fig. 5. Internal magnetic field distribution with and without compensation coils measured by magnetic-sensitive transition method

Fig. 6. Scheme diagram of the C-field and its compensation coils current supply circuit

Fig. 7. Fluctuations of output current and central frequency. (a) Output current fluctuation of the voltage regulator circuits; (b) fluctuation of (－1, －1) Ramsey transition central frequency

Fig. 8. Ramsey fringes. (a) Ramsey fringes of (－1，－1) magnetic-sensitive transition when voltage regulator circuits is C-field current; (b) Ramsey fringes of (－1，－1) magnetic-sensitive transition when the NI-4156 card is C-field current

Fig. 9. Fluctuations of output current and central frequency. (a) Output current fluctuations of the NI-4156 card; (b) fluctuation of the (－1, －1) Ramsey transition central frequency

Fig. 10. Allan variance after magnetic field optimization of rubidium fountain atomic clock