Buffer Gas Pressure Stabilization And Vacuum Sealing Experiments For Mercury Ion Microwave Clock

Mercury ion microwave clock based on buffer gas cooling has exceptional frequency stability,low drift rate and superior potential for continuous operation and miniaturization,which considered to be the prior choice for the next generation of deep space exploration and satellite navigation and positioning atomic clocks.It has wide application prospects in basic scientific research and engineering technology fields such as precision measurement,astronomical observation,satellite navigation and deep space exploration.The collision shift caused by the change of buffer gas pressure is the key factor that restricts the long-term stability of mercury ion microwave clocks.Therefore,measuring and evaluating the change of buffer gas pressure and realizing the stable control of gas pressure are of great significance for evaluating and improving the performance of mercury ion microwave clocks.We have systematically studied the key technologies of helium injection method,pressure monitoring and precise control,and realized the long-term stable control of buffer gas pressure.In addition,we used the neon as buffer gas,which has smaller collision shift.Then,sealed vacuum experiments were carried out to obverse the long-term evolution of neon and background gases in the sealed vacuum system.The main contribution of the dissertation is as follows:1.Accurate measurement of helium pressure and long-term stability control are realized.In view of the characteristics of the existing helium injection devices,the experimental factors affecting the helium injection rate are comprehensively analyzed,A helium constant pressure control device is proposed.The method can control the long-term fluctuation of helium pressure within 0.3%,which influence of helium collision shift on the long-term stability of the system is less than 1 x 10-15.2.The evolution of gas in sealed vacuum is studied and we design a compact prototype based on sealed vacuum.The sealed vacuum has realized long-term and energy-free maintenance based on getter pump.The trapping time is about 24 hours.The neon pressure in sealed vacuum clock decreases slowly with the time and it has different depletion rate under different neon pressure conditions.If has higher neon pressure in sealed vacuum chamber,the depletion rate would be higher too.The evolution of methane pressure reaches a stable value after 60 days.3.At present,the miniature mercury ion clock with this sealed vacuum system has realized closed-loop locking,and has achieved the frequency stability as low as 10-15.