Development of aperiodic multilayer mirrors operated at W-Lbeta line for plasma diagnostics application

Multilayer interference mirrors play a pivotal role in spectroscopic diagnostic systems, which probe electron temperature and density during inertial confinement fusion processes. In this study, aperiodic Mo/B4C multilayer mirrors of varied thicknesses were investigated for X-ray plasma diagnostics at the 9.67-keV W-Lbeta line. The thickness distribution of the aperiodic multilayers was designed using the 1st Bragg diffraction condition and then optimized through a simplex algorithm to realize a narrow bandwidth and consistent spectral response. To enhance spectral accuracy, further refinements were undertaken by matching the grazing incidence X-ray reflectivity data with actual structural parameters. X-ray reflectivity measurements from the SSRF synchrotron radiation facility on the optimized sample showed a reflectivity of 29.7% ±2.6%, flat-band range of 1.3 keV, and bandwidth of 1.7 keV, making it suitable for high-temperature plasma diagnostics. The study explored the potential of predicting the 9.67 keV reflectivity spectrum using the fitting data from the Grazing incidence X-ray reflectivity (GIXRR) curves at 8.05 keV. Additionally, the short-term thermal stability of an aperiodic multilayer was assessed using temperature-dependent in situ X-ray measurements. Shifts in the reflectivity spectrum during annealing were attributed to interdiffusion and interfacial relaxation. The research team recommends the aperiodic Mo/B4C multilayer mirror for operations below 300 ℃.