Two-Photon Absorption Laser-Induced Fluorescence Investigation of CO2 Plasmas for Mars Entry

Abstract

Two-photon absorption laser-induced fluorescence measurements have been conducted to investigate atomic oxygen temperature and number density in a CO 2 plasma relevant to Martian entry. The high-enthalpy plasma flow has been produced by an inductively heated plasma generator. This paper describes the experimental setup and shows the applicability of laser diagnostics to Mars-relevant plasmas. Particular emphasis is put on the use of the generated data for the numerical simulation of the aerothermal chemistry of a Martian entry. Relative fluorescence signals are calibrated by a procedure using xenon as a reference. This calibration method allows the in situ experimental determination of the instrumental broadening of the spectroscopic setup and thus an accurate temperature measurement. The acquired, highly resolved line profiles of the fluorescence signal yield a translational temperature of 2777 K 400 K and a mean number density of 1.55 · 10 19 m −3 60%. Nomenclature= molar mass of oxygen _ m CO 2 = CO 2 mass flow n = number density N A = Avogadro constant P el = electrical power p amb = ambient tank pressure Q = quenching coefficient S = fluorescence signal T tr = translational temperature U = voltage η = transmissivity and quantum efficiency factor λ = wavelength σ 2 = absorption cross section

Aerothermodynamic Investigation of Inductively Heated CO2 Plasma Flows for Mars Entry Testing

“…The findings on translational temperature and number density measurements by TALIF have recently been published. 22 These results will be supplemented by the following TALIF velocity measurements. For a more detailed description of the analysis procedures and results the reader is kindly referred to Marynowski et al 22 With TALIF a particular excitation state of a species is actively probed using a laser.…”

“…22 These results will be supplemented by the following TALIF velocity measurements. For a more detailed description of the analysis procedures and results the reader is kindly referred to Marynowski et al 22 With TALIF a particular excitation state of a species is actively probed using a laser. The excited species falls back to a lower energy level and this fluorescence emission is measured using an appropriate photo detector and spectral bandwidth filters to separate the fluorescence signal from other plasma emissions.…”

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

“…But its simplicity and high return on investment still governs over more elaborate techniques such as for example laser-induced fluorescence (LIF) spectroscopy, which is difficult to carry out near the surface during ablation analysis. Although LIF spectroscopy has successfully been applied to the investigation of ground state species populations in the plasma freestream 39,40 . These can be detected with this setup.…”

Review of Heat Flux Measurements for High Enthalpy Flows

“…The experiments produce high enthalpy flows representative of the aerothermodynamic environment encountered during atmospheric entry of Earth, Mars, Venus and Titan. [3][4][5][6][7] The testing logic is to reproduce the stagnation line boundary layer aerothermochemistry of the flight in the ground based facility. 8,9 Therefore, local physical parameters of the flow need to be assessed, such as local mass-specific enthalpy and spatially resolved boundary layer temperatures and number densities.…”