Near Surface CO2 Detection in an Inductively Coupled Plasma Facility Using Diode Laser Absorption

Abstract

Uncertainty exists as to whether appreciable amounts of CO2 are formed by surface recombination for Mars entry vehicles. It is well understood that highly catalytic thermal protection system (TPS) material can lead to nearly two times the heat flux to the vehicle surface as a non-catalytic material. Conservative design practice assumes a supercatalytic surface to accommodate this uncertainty. Risk avoidance leads to oversized TPS geometries that add mass to entry vehicle designs that could be otherwise employed. Determining whether significant near surface production of CO2 occurs at trajectory heating conditions would add significant insight. The University of Vermont (UVM) has developed a 30kW Inductively Coupled Plasma (ICP) Facility to provide a pure high temperature plasma environment for aerospace material testing and gas-surface interaction chemistry investigations. The goal of the present work is to develop and test a diode laser absorption spectroscopy (DLAS) sensor to target near sample surface CO2 concentrations. A DFB diode laser at 2744 nm with a tuning range of around 3 nm is chosen as the light source. Current investigations show no appreciable amount of CO2 near a highly catalytic surface (water cooled copper) within the sensors' detectivity limits. Work is ongoing to further improve these sensitivity limitations.

Near-Surface Carbon-Dioxide Tunable Diode Laser Absorption Spectroscopy Concentration Measurements in Hypervelocity Flow

“…Although this study focuses on an aluminum cylinder, these low recombination efficiencies are consistent with diffusion tube measurements on a variety of metal surfaces, indicating that surface reactions are not dominated by the reaction pathway leading to formation of CO 2 [44]. Preliminary measurements using an inductively coupled plasma facility also show minimal amounts of CO 2 near a highly catalytic water-cooled copper wall [45].…”