## 2 Experimental Setup  
Using the Shanghai-EBIT [61; 62], the measurements were conducted in a Xenon-dominated plasma environment with negligible Doppler shifts. In a vacuum environment better than 10\({}^{-10}\) torr, a quasi-monoenergetic electron-beam, accelerated by an electric field and compressed by a magnetic field, undergoes continuous collisional ionization and excitation with externally injected Xenon in the trap region. The highly charged Xenon ions were produced and confined in the trap region by the axial electric potential, a magnetic field, and the space charge effect of the electron-beam, forming a high-temperature plasma light source along with the incident electrons. In these experiments, the electron-beam energies were set between 5.5 keV and 7.6 keV, exceeding the ionization energy to produce Ne-like Xe at 3.33 keV [63] but slightly lower than that of F-like Xe at 7.66 keV [64], resulting in a charged state distribution dominated by Ne-like Xe. The electron-beam energy conditions were chosen based on the level structure of Ne-like Xe [65] to activate different cascade transition channels at each condition, leading to significant variation in emission intensity. The electron-beam energy was determined by the potential difference between the emission cathode and the drift tube, which is modified by the space charge effect in reference to previous studies [66; 67; 68]. During the experiments, the beam-current was maintained between 42 mA and 48 mA. Table 1 presents the main operating parameters of the Shanghai-EBIT in these experiments. The width of electron-beam in the trap region was measured by a slit imaging system [69], allowing the inference of the electron density in the trap plasma. Typical beam width and electron density values in these experiments are 73 \(\upmu\)m and 1.6 \(\times\) 10\({}^{12}\) cm\({}^{-3}\), respectively. Spectra of xenon were obtained using a high precision flat crystal spectrometer with a nominal resolving power of approximately 6500 [70], which is sufficient for resolving the lines of interest in our experiments. The oil-free rotatable feedthrough system in the crystal spectrometer creates a favorable vacuum environment, enabling direct coupling with the EBIT main chamber without the need for isolation film. This setup avoids any impact on line-intensity measurements caused by absorption from isolation film. The spectrometer was equipped with a 5.0 \(\times\) 2.5 \(\times\) 0.5 cm\({}^{3}\) Si(111) crystal, with the lattice constant of 2\(d\) = 6.2712 A. The Bragg angle was set to approximately 25.8\({}^{\circ}\) for measuring the wavelength region near 2.71-2.78 A. The spectra were recorded by a CCD with 2048 \(\times\) 2048 pixels (pixel size \(\Delta\)x = 13.5 \(\upmu\)m). Due to the energy difference between the 3D and 3F transitions being within 0.3%, the impact of the crystal reflectivity and the CCD's quantum efficiency on intensity measurements can be neglected. Data accumulation time ranging from 14 to 34 h were conducted at each energy condition. To enhance the reliability of intensity measurements, the two-dimensional pixel count arrays obtained through CCD accumulation were reconstructed by photonization and \begin{table}
\begin{tabular}{c c c} \hline \hline \(E_{e}\) (keV) & \(I_{e}\) (mA) & Time (h) \\ \hline
5.50 & 42.3 & 34 \\
6.00 & 47.8 & 18 \\
6.35 & 45.0 & 22 \\
6.70 & 48.5 & 28 \\
6.90 & 47.0 & 20 \\
7.20 & 48.3 & 14 \\
7.60 & 48.0 & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: EBIT operation parameters (electron-beam energy, current, and accumulation time). filtered by count threshold using a data processing program. This program can significantly improve the signal-to-noise ratio of the spectra, thus it has been widely employed in X-ray spectroscopy measurements in our laboratory [71; 72]. In the spectral processing for these experiments, count thresholds were set according to the principle of less intensity loss and baseline normalization.