Experimental Validation of Emissivity-Independent Statistical Pyrometry for MPD Thruster Cathode Diagnostics

Abstract

This thesis presents the development and experimental validation of an emissivity-independent statistical pyrometry method for high-temperature diagnostics, with a focus on applications involving magnetoplasmadynamic (MPD) thruster cathodes. Conventional optical pyrometry techniques rely on assumed or known emissivity, which may introduce significant uncertainty in environments where emissivity is unknown or varies with wavelength and temperature. To address this issue, a multi-wavelength statistical model is proposed that reconstructs temperature by minimizing dispersion across pairwise wavelength combinations using Wien's approximation, while simultaneously estimating emissivity behavior. The method is first validated using synthetic datasets with defined emissivity models, demonstrating accurate temperature reconstruction and robust recovery of spectral emissivity trends under controlled noise conditions. The approach is then applied to experimental data collected using a refurbished four-color pyrometer system and a spectrometer-based setup, both calibrated with a tungsten ribbon lamp over the temperature range 1300–2300∘C. The results show that the statistical method consistently reconstructs temperature with greater stability than conventional approaches, particularly at higher temperatures, where Wien's approximation is most applicable. Although deviations are observed at shorter wavelengths due to increased noise sensitivity and exponential error amplification, the overall spectral trends in emissivity are preserved, supporting the use of simplified emissivity models. The study also identifies limitations, including restricted wavelength coverage and calibration biases, especially in discrete-filter pyrometry systems. To summarize, this work demonstrates the feasibility of emissivity-independent temperature measurement using limited spectral data and establishes a validated framework for high-temperature diagnostics in plasma propulsion environments.