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Experimental and analytical investigations were conducted to predict the wear of the discharge cathode keeper orifice in the NASA Evolutionary Xenon Thruster. The ion current to the keeper was found to be highly dependent on the beam current, and the average keeper ion current density was nearly identical to that of the NASA Solar Electric Propulsion Technology and Applications Readiness (NSTAR) thruster for comparable beam current density. The ion current distribution was highly peaked toward the keeper orifice. The wear assessment predicted keeper orifice erosion to the same diameter as the cathode tube after processing 250 or 460 kg of xenon, depending on whether warm or cold ions, respectively, were assumed. Although the presented simple wear analysis does not predict failure, comparison with the NSTAR extended life test results suggests that the discharge cathode assembly will continue to operate beyond the qualification goal of processing 405 kg of propellant. Probabilistic wear analysis showed that the ion energy at the keeper surface and the sputter yield contributed most to the uncertainty in the wear assessment. It is recommended that fundamental experimental and modeling efforts focus on accurately describing the plasma potential, ion temperature, and the sputtering yield.

Wear Testing and Analysis of Ion Engine Discharge Cathode Keeper