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Characterization of LaB6 Emitters in an Inductively Coupled Plasma Facility for Electron Transpiration Cooling
Stunkel, Brian D.
Stunkel, Brian D.
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Abstract
A platform was developed to determine the applicability of Lanthanum Hexaboride(LaB6), a low work function material, for Electron Transpiration cooling (ETC) purposes. This study investigates the behavior of the material when exposed to conditions similar to those of hypersonic flight or atmospheric reentry in the University of Vermont 30 kW Inductively Coupled Plasma (ICP) Facility. Results from LaB6 ETC performance are compared to that of a common relatively low work function material - POCO graphite, as well as velocity impacts on ETC performance through use of a converging flow augmentation nozzle. The study also includes a full plasma characterization test suite, testing the plasma heat flux, Local Thermodynamic Equilibrium (LTE) temperature, and electron density the ETC probe is exposed to at all testing conditions. Post-testing results from Scanning Electron Microscope (SEM) imaging of the LaB6 ETC samples are also described. Initial results suggest that the LaB6 material shows improved ETC performance when compared to similar POCO graphite samples, as well as increased performance at higher plasma flow velocities from the converging nozzle. The LaB6 material was notably shown to generate considerable oxide scale after testing, which is shown in imaging. Heat flux results showed the impact of varying the sizing of the heat flux collection device, and allowed for evaluation of impacts of the nozzle geometry on the heat flux of the plasma jet. LTE temperature results were in relative agreement with previous studies, although showed the impact of several significant measurement problems and inconsistencies. The same was true of electron density comparisons, although these showed strong agreement with theoretical Chemical Equilibrium with Applications (CEA) generated models in the plasma jet-center region.
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Date
2026