## 3 Results
### Tunning for XAS  
XAS is a widely used experimental technique that is performed at synchrotron radiation facilities for research in material science, chemistry, and biology [34]. The XAS experiment uses TEY measurements, which measure the absorption of X-rays by considering a sample as a function of energy. During the experiment, along with the incident energy changes, the intensity of the X-ray before and after the sample are recorded and normalized to obtain the absorption coefficient. The absorption spectrum provides information about the electronic and atomic structure of the sample, including oxidation state, coordination number, and bond length.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Energy (eV)** & 300 & 460 & 700 & 920 & 1200 & 1500 & 1800 \\ \hline
**V\({}_{0}\)** & 0.0399 & 0.0467 & 0.0353 & 0.0475 & 0.0453 & 0.0431 & 0.0448 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The minimum threshold value for different incident X-ray energy.  
Figure 7: The measurement result of the left and right blade-edge signals, along with the M2 position changes at 920 eV. The minimum moving precision of the M2 motor is 200 nm. The experimental data were fitted with a straight line, and the linear area slope shows the position changes of S\({}_{\rm RL}\) changes as M2 moves per 200 nm. It is found that the threshold value is less than 0.05.  
The normalized absorption spectrums of an Fe sample holder with and without the online automatic feedback system are shown in Figure 9. The intensity of the X-ray before the sample position during the experiment, which is collected by the gold mesh, is displayed at the top right of Figure 9.  
Data acquisition for each spectrum takes about 10 min. Without the feedback system, the intensity of the feedback from the data (top right subfigure of Figure 9) drops quickly  
Figure 8: Operation interface of the online automatic feedback system. Beamline Monitor panel displays energy, M2 position, \(\mathrm{S_{L}}\), \(\mathrm{S_{R}}\), \(\mathrm{S_{U}}\), \(\mathrm{S_{D}}\), \(\mathrm{S_{V}}\) and \(\mathrm{I_{0}}\); Config Panel is used to input M2 step, offset, \(\mathrm{V_{0}}\) configuration with a running button and data export components; the Chart Area on the right side displays all signals with a maximum time span of 12 h.  
Figure 9: XAS experiments using TEY measurement in the absence and presence of the feedback system. The normalized absorption coefficient has a higher signal quality when the feedback system is on. The top right figure shows that the X-ray flux with the feedback system on drops much slower and smoother.  
during the energy scan. However, with the feedback system, the intensity drops much slower and smoother. The normalized absorption coefficient in the feedback on the spectrum is also consistently higher than the feedback from the data across the entire energy range with a higher signal quality. We conducted signal-to-noise ratio (SNR) calculations on the normalized data within the energy range of 724 eV to 730 eV, where the feedback system had optimized the M2 position. The SNR for the feedback from the data is 55.390 dB, whereas the SNR for the feedback from the data is 57.351 dB, resulting in an improvement of nearly 2 dB in the SNR. These results demonstrate the effectiveness of the feedback system in improving the quality of the XAS data by maintaining a stable X-ray intensity during the experiment. The improved data quality can lead to more accurate and reliable results, making it an essential tool for XAS experiments.