Fast Surface Temperature Measurement of Teflon Propellant in Pulsed Ablative Discharges Using HgCdTe Photovoltaic Cells (PREPRINT)

摘要

High speed Mercury Cadmium Telluride photovoltaic detectors sensitive to infrared emission are investigated as a means of measuring real-time surface temperature on a micro-second timeframe pulsed ablative discharge with Teflon(TradeMark) as the ablated material. Analysis is used to derive a governing equation for detector output voltage for materials with wavelength dependent emissivity. The detector output voltage is experimentally calibrated against thermocouples embedded in heated Teflon. Experimental calibration is performed with Teflon that has been exposed to '200 pulsed discharges and non plasma-exposed Teflon. These are compared to theoretical predictions to analyze emissivity differences between plasma-exposed and non plasma-exposed Teflon. The diagnostic capability is evaluated with measurements of surface temperature from the Teflon propellant of electric micro-Pulsed Plasma Thrusters. During the capacitive discharge, there is insufficient information to claim that the surface temperature is accurately measured. However, immediately following the discharge, the post-pulse cooling curve is measured. The statistical spread of post-pulse surface temperature from shot-to-shot, most likely due to arc constriction and localization, is investigated to determine an operational envelope for post-pulse temperature and mass ablation. This information is useful for determining post-pulse ablation contributions to mass loss as well as evaluation of theoretical discharge models currently under development.