Study And Realization On QXAFS Data Acquisition System Based On EPICS At SSRF

With the appearance and development of the synchrotron radiation, various kinds of newsynchrotron radiation experiments are springing up constantly. Developing new synchrotronradiation experimental methods and utilizing them to carry out research works on related fieldshave become an important application content of the synchrotron radiation. X-ray Absorption FineStructure (XAFS) is a powerful structure analysis method which grows up with the developmentof the synchrotron radiation.Different from the conventional XAFS experimental method which adopts “step-by-step”data acquisition mode, the Quick-scanning XAFS (QXAFS) experimental method employs“on-the-fly” mode to carry out the data acquisition process. The QXAFS experimental method iscapable of obtain the QXAFS spectrum of the experiment sample in the process of the continuousmovement of the Double Crystal Monochromator (DCM). QXAFS experimental method cancomplete to acquire a XAFS spectrum in the second scale and it is very suitable to study thedynamic in suit process in the fields of catalyst industry, chemical process, biosensor and materialscience. Comparing to other time-resolved XAFS methods, such as Energy-Dispersive XAFS,pump-probe XAFS et al, the QXAFS method has a good compatibility with the conventionalXAFS method and it doesn’t need to change the structure of the beamline stations. It is verysuitable to carrying out the study on the time-resolved XAFS experimental method for XAFSbeamline at the Shanghai Synchrotron Radiation Facility (SSRF).Based on widely investigation and survey of the QXAFS data acquisition system at relatedhome and abroad beamlines, we carry out the research on the QXAFS data acquisition systembased on EPICS. The work mainly includes:1. The overall design scheme which unifies the motion control and QXAFS data acquisitionsystem has been achieved. It aims at solving the drawbacks of the current QXAFS data acquisitionsystem of the XAFS beamline at SSRF. The Scaler is used to acquiring the X-ray energy byrecording the counts of the control pulses for the stable Bragg motor in the system scheme. Thehigh-speed ADC is adopted to acquire X-ray current signals of the front and back ionizationchambers. There is a stand-alone hardware trigger signal source which provides two1MHz hardware trigger signals for the ADC and Scaler and realizes the hardware synchronizationbetween the control and data acquisition systems. The hardware configurations, softwaredevelopments and offline tests of the three parts have been accomplished in the laboratory. Finally,the integration and the system unit debug of the whole QXAFS data acquisition system have beenfinished.2. We have carried out the study and online test on the QXAFS data acquisition system at theXAFS beamline stations at SSRF. The experimental conditions which can improve thesignal-to-noise ratio of the QXAFS experimental method were studied and summarized, includingselecting the sample rate of the ADC, determining the subdivided numbers of the Bragg motordrivers and compensating the T2motor at the energy scanning periods. We have studied theimpacts of different parameter configurations of the current amplifier on the QXAFS spectra anddifferent integration time on the high energy zone of the QXAFS spectra. The comparison with theconventional XAFS spectra of the7.5um standard copper foil prove the QXAFS data acquisitionsystem not only have a high acquisition speed and good signal-to-noise ratio, but also a goodstability and repeatability.We have carried out the research on the in situ process of the gold nanoclusters adding thehydrochloric acid etching reaction. We have obtained the QXAFS spectrum at different momentsin order to grasp the etching mechanism of Au8cluster adding hydrochloric acid. The experimentresults show that the small gold nuclear atom number of the Au8clusters and the less obviousAu-Au coordination peak. Because the nonmetallic coordination peak changes greatly only at theinitial of the reaction, the experiment results indicated the reaction speed was too fast. We need totry to reduce the speed of the reaction in order to obtain more abundant information during thereaction. The application study confirms the QXAFS data acquisition system based on EPICSmeets the requirements for carrying out the research on dynamic in situ process.