Online

Schindler, Jeffrey C

Mechanical Engineering

2021

M.S.

A vehicle reentering Earth's atmosphere at hypersonic velocities violently compresses the air in front of it, creating a shell of plasma at the surface. This plasma imparts energy onto the vehicle's surface via convective, radiative, and chemical heating. Currently, large uncertainties in measurements of surface reaction rates lead to over-designed thermal protection systems. Improvements in the precision of these measurements could substantially decrease the weight of the heat shield, freeing up space for additional fuel or human/scientific payload. This work aims to improve current methods for measurements of atomic number densities in plasmas, so that they may be applied to future measurements of surface reaction rates. In this work, relative number densities are measured by probing atomic species in an inductively coupled plasma with two-photon absorption laser induced fluorescence. The use of a room temperature flow reactor as a reference source allows for absolute calibration of relative number density measurements while removing many constants, and their uncertainties, from the calculation. Temperature and number density measurements in the free stream of air and nitrogen plasmas suggest near equilibrium populations of both oxygen and nitrogen atoms. Improvements in methods for fluorescence lifetime measurements, allow for resolution of the lifetimes between 1.5 and 4 ns which are seen in the plasma. Evidence of collision-induced upper state transfer in the plasma is presented. Off line center excitation of N, O, and NO show evidence of higher quenching than is seen at the line-center. Further work is needed to determine if this is a physical phenomenon, or instrumental error.