Energy shortage is a global challenge, and inertial confinement fusion (ICF) may offer a potential solution. The development of high-temperature, high-density plasma physics is critical for advancing thermonuclear fusion research and plays a significant role in addressing energy problems. In high-temperature, high-density plasma diagnostic experiments, X-ray spectroscopy plays a crucial role. By analyzing the X-ray emission and absorption spectra, detailed information about plasma temperature, density, and other key parameters can be obtained. Crystal diffraction of X-rays is the primary method for spectral detection. The accuracy of the diagnostic results depends on the spectral resolution, diffraction intensity, and photon throughput of the crystal spectrometer. Therefore, an ideal spectrometer must have high photo throughput and high energy resolution across a wide spectral range. Cylindrical and conical crystal spectrometers may achieve high photon throughput across a wide spectral range. However, the difference in optical path lengths can adversely affect diagnostic results, and these spectrometers cannot mitigate the influence of source broadening on spectral resolution. Spherical and toroidal crystal spectrometers can meet these requirements but are limited by a narrow measurable spectral range. Based on the theory of Rowland circle bent crystal diffraction focusing, we propose a multi-Rowland-circle bent surface structure, enabling spectrum diagnosis with high photon throughput and high spectral resolution across a wide spectral range.

The Rowland circle structure significantly reduces the influence of source broadening on spectral resolution. To further improve this, a multi-Rowland-circle structure is used instead of a single Rowland circle. By designing the diffraction positions for multiple energy points on the curved crystal, several ideal imaging points are achieved. High spectral resolution is possible for all energy points across a wide spectral range. In addition, the rotational symmetry of the diffraction circle provides excellent photon collection efficiency. The combination of multiple diffraction circles corresponding to different energy points forms the curved surface of the crystal. The multi-Rowland-circle structure eliminates Johann error, minimizes the influence of source broadening, and enables high-efficiency focusing across a wide spectral range.

The detection system designed in this paper covers Bragg angles from 32.1° to 36.5°, corresponding to a spectral energy range of 7.6 keV to 8.5 keV (Fig. 2). The crystal model dimensions are 61.3 mm×42.0 mm×20.9 mm, and the material is α-quartz (2023). In the theoretical design, the distance from the light source to the crystal center is 280 mm, and the distance from the crystal center to the detector is 838.8 mm, providing ideal distances for system focusing and imaging. Spectral focusing experiments of the multi-Rowland-circle bent crystal structure target the Kα1 and Kα2 spectral lines of Cu. The theoretical spectral resolving power of the system is calculated to be 7300, with the detector resolution set at 100 μm. X-ray diffraction simulations are conducted using X-ray crystal diffraction (XCD) software for the multi-Rowland-circle structure. These simulations focus on the Kα1 and Kα2 X-ray lines of Cu (Fig. 3). The simulation results show excellent focusing performance when the detector is placed at the ideal position. The source includes seven energy points in the range of 7.6 keV to 8.5 keV, and the focused images of these points are obtained when the detector is in the optimal position (Fig. 4). This confirms that the multi-Rowland-circle crystal can achieve diffraction focusing across the designed energy range, demonstrating the spectrometer’s capability for wide-spectrum detection. Further tests on varying the size show that spectral resolving power remains stable, effectively suppressing the influence of source broadening (Fig. 5). In the simulation experiments when the detector resolution is set to 100 μm, the system’s spectral resolving power is calculated to be around 5000 (Fig. 6). The hygroscopic nature and anisotropy of certain crystal materials makes fabrication challenging. The manufacturing process of the multi-Rowland-circle bent crystal involves two steps: first, the crystal substrate is fabricated, and then the crystal is bonded to the substrate using intermolecular forces and adhesive. This method makes the spectrometer less susceptible to environmental factors such as temperature, humidity, and vibration. Spectral tests are conducted on a test platform using a Cu target X-ray tube. The multi-Rowland-circle bent crystal serves as the diffraction device, and a CMOS detector is used for X-ray detector. The experimental results are consistent with the simulation results, and focused images of the Cu Kα1 and Kα2 lines are obtained (Fig. 9). When the detector is positioned ideally, well-focused X-ray images are achieved. The actual spectral resolving power of the crystal spectrometer is calculated at 3010 (Fig. 10). Despite using a low-power X-ray source (24 kV and 0.1 mA) and a short exposure time (1 s), high-brightness focused images are obtained, demonstrating excellent photon throughput. However, due to limitations in the crystal surface accuracy, the actual spectral resolving power deviates slightly from the theoretical value. Therefore, future research will focus on refining crystal surface fabrication techniques to further improve the system’s spectral resolving power and photon throughput.

Based on the Rowland circle structure, we introduce a multi-Rowland-circle structure to extend the spectral detection range. This design enables our detection system to achieve both high photon throughput and high spectral resolving power across a wide spectral range. To validate the theory, we conduct X-ray simulation experiments, followed by the development and testing of the multi-Rowland-circle crystal. Both simulation and experimental results demonstrate that our detection system exhibits excellent focusing performance and high photon throughput within a certain spectral range, effectively focusing rays into bright points. Moreover, it significantly suppresses the influence of source broadening on spectral resolving power. The actual spectral resolving power reaches over 3000, indicating our system’s high spectral resolving power.