Inductively Heated Air Plasma Flow Characterization with Laser-Induced Fluorescence Measurements

Abstract

T HERMAL protection systems for Earth reentry maneuvers are currently being qualified bymeans of plasmawind tunnels. The latter generate high enthalpy air plasma flows as expected for the reentry missions [1,2]. The progress in the development of future thermal protection systems (TPS) as, for example, toward the development of reusable systems, inherently depends on the understanding of the material behavior [2]. Here, especially the catalycity of the selected TPS material is of significant influence. To investigate the catalytic behavior, a stationary pure high enthalpy airflow is needed. Conventional arcjets contaminate the air plasma flow with electrode erosion products similar to copper or tungsten possibly leading to a change in the catalytic material’s behavior during the TPS qualification process. Hence, electrodeless inductively heated plasma generators are advantageous for material investigations as well as for investigations with respect to the impurities of the plasma flow of conventional plasma wind tunnels. In this paper, results of laser-induced fluorescence (LIF) measurements of atomic oxygen in an inductively heated air plasma flow are presented. The experimental and theoretical approaches are described in detail in previous publications [3,4]. The measurements presented in this paper are the first results of an extension of the setup to air plasma conditions. The measurements are of particular importance for comparison andvalidationof futureflight experiments as, for example, the pyrometric heat flux experiment (PHLUX) on the European experimental reentry test bed (EXPERT) [5]. The excitation is performed using a pulsed laser system and the fluorescence is detected using a photomultiplier and a fast oscilloscope as well as gated integrators. Oxygen atoms in the ground electronic state are excited via the 3pP2;1;0 2pP2 twophoton transition at about 225 nm. The resulting fluorescence is measured using the 3pP2;1;0 ! 3sS1 transition at 844.5 nm.