Development of a Stark shift measurement technique using excited-state oxygen atoms to determine electron number density in shock heated O <sub>2</sub> /Ar above 10 000 K
Yang Li, Shengkai Wang, Christopher L. Strand, Ronald K. Hanson
Abstract
Abstract We present measurements of electron number density, n e , in partially ionized gases containing electronically excited atomic oxygen, at nominal translational temperatures between 10 100–11 200 K. The measurements were based on the Stark shift of the O( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mmultiscripts> <mml:mrow> <mml:mtext>P</mml:mtext> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:none/> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> ) to O( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mmultiscripts> <mml:mrow> <mml:mi mathvariant="normal">D</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn> <mml:mo>,</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> ) transition at 926 nm. The current work scanned the laser across the transition and utilized the Stark shift of the absorbance for robust determination of n e . The measurements were conducted in a shock-heated 1% O 2 /Ar mixture, with a measurement time resolution of 20 μ s. A line-center shift of −0.06 cm −1 was observed within around 500 μ s of the test time after the mixture was instantaneously heated to 11 200 K by the reflected shock wave, which corresponded to an electron number density increase from 0 to 2 × 10 21 m −3 due to collisional ionization. The measurement method and resulting data may be of interest in future studies of high-temperature air flows.