Quantitative optical emission spectroscopy monitoring of Erosion product in hall thruster channels based on composite line Actinometry

AbstractOptical emission spectroscopy (OES) method has been widely employed for monitoring ceramic channel erosion products in Hall thrusters. Analysis of OES results relies on actinometry, which requires spectral lines with similar excitation energies. However, the absence of Xe I lines matching the excitation energy of the B I lines of erosion products in Hall thrusters imposes significant limitations on traditional actinometry. To address this, this work proposes a composite line actinometry method. By constructing ratios from multiple spectral lines, the method effectively decouples the relative density of boron erosion product from the electron temperature, which is a major source of uncertainty. By investigating a 100 W Hall thruster, the composite line ratio is constructed using Xe I lines at 881.94 nm and 992.32 nm, along with B I line at 249.77 nm. Results demonstrate that when the electron temperature ranges between 5 and 15 eV, the boron atoms' relative density derived from the measurements remains unaffected by electron temperature and is exclusively determined by the composite line ratio. Compared to traditional actinometry, the composite line actinometry reduces quantification deviations in erosion characteristics by 10–38% under varying acceleration voltages and by 4–25% under varying mass flow rates. This work establishes a robust OES-based framework for the relative measurement of erosion rate at different operation conditions, building a direct correlation between spectral signals and erosion characteristics, enhancing the capability of OES for real-time assessment in Hall thrusters, providing stronger support for lifetime and reliability evaluation.