| Time-of-flight secondary ion mass spectrometry(TOF-SIMS) is one of the mass spectrographs, and it is featured by a simple structure, high sensitivity and a wide range of quality testing, etc., with good prospects for development. This paper is made based on the major national scientific instrument and equipment development project: the dedicated scientific TOF-SIMS apparatus for isotopic geochronology, which is aimed to apply TOF-SIMS technology to the field of high-precision isotope ratio analysis, so as to solve the micro-situ analysis problem of stable isotope and rare-earth element in universe sample and rare geochemistry sample. The use of TOF-SIMS needs to design the ionflow controlling circuit so that the ion beam will fly follow the designed path. Ion beam deflection power supply and vacuum measuring control system are integral parts of the ion-flow controlling circuit of the dedicated scientific TOF-SIMS facility for isotopic geochronology.The ion beam deflection power supply is used to control the fly direction of the ion beam and calibrate its fly path, making up the processing errors of mechanical parts. For this reason, the ion beam deflection power supply shall be equipped with the following features: dual channels and symmetric output, and the output of-250 V ~ + 250 V continuous adjustable DC voltage. At the same time, TOF-SIMS has extremely strict requirements of parameters of the ripple and symmetric dual- output of the ion beam deflection power supply. In order to achieve the functional needs and indicative needs of the dedicated scientific TOF-SIMS apparatus for isotopic geochronology on onion beam deflection power supply, this paper develops a symmetric double-output power supply controlled by-10 V ~ + 10 V voltage signals to output-250 V ~ + 250 V voltage. The power supply uses a multi-stage amplifier circuit to increase the internal resistance and fine adjust the magnification; uses integral circuits and introduces an adjustable bias voltage to adjust the static operating point of the power supply; uses a relatively novel closed-loop negative feedback circuit to achieve the operational amplifier of input voltage signals and the suppression of output ripple; uses an adjustable reverse phase proportional amplifying circuit to realize the symmetric dual-channel output. When the design of ion beam deflection power supply is completed, the author will use Multisim software to make a software simulation of the completed power supply to determine its feasibility. Then, the author will draw and print the circuit board and weld as well as debug the board. Finally, the author will use the Solidworks software to design a case for the ion beam deflection power supply and install the circuit board to the case to complete the development of the ion beam deflection power supply. After that, key parameters of the power supply, including the ripple, dual-output voltage difference and output symmetry will be tested, and the test result show that all key parameters basically meet the requirements: symmetric dual-output,-250 V ~ 250 V continuous adjustable voltage; the output ripple peak is smaller than 10 m V, with the effective value smaller than 5m V; the maximum output voltage difference is smaller than 0.25 V and the output symmetry is less than 0.12%. Currently, the ion beam deflection power supply has been applied to four developed dedicated scientific TOF-SIMS apparatuses for isotopic geochronology.Since ultrahigh vacuum is a necessary condition for the formation of an ion beam, all SIMS instruments need a vacuum measuring control system to control their various vacuum components, thus achieving the ultrahigh vacuum and the real-time monitoring of the vacuum. Since the advanced foreign instrument is of a structure different from that of SIMS, its designed scheme of vacuum measurement and control system cannot be directly applied to the subject project and then it needs to refer to design scheme of same instruments and the supporting vacuum measurement and control system. Firstly, this paper makes a need analysis to determine the design of vacuum measuring control system. Then, the system is designed based on the selected scheme in terms of the chip selection, schematic design and software design. In this paper, the STM32F103 is taken as a master chip to achieve the control of peripheral circuits including the serial-interface expansion circuit, RS485 level switching circuit, RS232 level switching circuit, human-computer interaction circuit and vacuum components circuit. The GM8125 serial-interface expansion chip is used to expand the 232 bus to eight branches so as to achieve the control of four vacuum gauge controllers and four mechanical pumps; the RS485 bus is used to control four sub-pumps; and a remote relay is used to control four vacuum valves. Finally, this paper presents an intelligent vacuum control strategy, hoping to offer a solution for the future improvement of the vacuum measuring control system. |
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