The Hydrogen Atom Beam Flux Control System Of Passive Hydrogen Maser

The long-term stability of hydrogen maser is mainly limited to the systematic effects, including the variation of hydrogen atom beam flux, cavity pulling effect, wall shift and second-order Doppler effect, etc. While the short-term stability depends on the basic thermal noise of system. To further improve the frequency stability of hydrogen maser, it's necessary to consider the impacts of all aspects and make improvements. This paper proposed that the stability of hydrogen atom beam flux must be limited to 5% by analyzing its effects on the frequency stability of hydrogen maser, and designed the control system.This dissertation analyzed the gas flux characteristics in the vacuum system of hydrogen maser, and presented the hydrogen atom beam flux measurement could be changed into the measurement of system vacuum degree. After comparing various vacuum measurement methods, the system selected to measure the vacuum degree according to the heat conducting principle of vacuum gauges, and made a demonstration. Finally, this article designed the closed-loop control system based on the testing of vacuum degree, which could control the hydrogen atom beam flux by adjusting the heating power of the palladium-silver alloy tube.The system first designed the hydrogen atom beam flux measurement circuit, chose C8051fl21 MCU as the core controller, then designed the relative circuit module, including the ambient temperature detection module, flux given module, PWM controlled heating module, data communication module and power module. And then designed the software to implement data acquisition and processing, and to realize the communication function of the microcontroller and upper computer. After the completion of the experimental platform construction, the system compared the common PID algorithm with the Dahlin algorithm, and selected the latter as control algorithm, then determined the control parameters of Dahlin digital controller and control processes. Finally, a series of hydrogen atom beam flux control experiments was designed and conducted to evaluate the control performance of system. The experimental data indicates that the system can implement the hydrogen atom beam flux regulation, control precision better than 99.56%, relative stability better than 2%, good repeatability, can meet the design objective.