Metastable oxygen atom velocity and temperature in supersonic CO₂plasma expansions

Abstract

Radial and axial velocity distribution functions of 5 S o 2 metastable oxygen atoms were obtained by way of resonant laser induced fluorescence spectroscopy at 777.19 nm in rarefied supersonic plasma jets produced from pure CO 2 and CO 2-N 2 gas mixtures. The N 2 seeded fraction is 3% in volume in order to mimic the Martian atmosphere composition. The measured lineshapes allow computation of the mean radial velocity and the perpendicular temperature, with respect to the jet axis, as well as the mean axial velocity and the parallel temperature. With an arcjet plasma source input power of 6.5 kW, the metastable O(5 S) atom axial velocity is around 4500 m s −1 and the atom perpendicular temperature reaches 4500 K at the nozzle outlet. Under identical voltage and current conditions, a small addition of N 2 does not change the measured values, i.e. it does not modify the overall energy balance. Distribution of flow parameters along both the radial and the axial directions reveals the existence of a barrel shock wave and a stationary shock front, which originate in shock wave regular reflexion. Flow properties, shock wave structure, departure from thermal equilibrium and impact of the applied power are debated for the two gas mixtures. Finally, the capacity of supersonic plasma expansions to simulate interplanetary probe entry into the Martian atmosphere is discussed in the light of experimental outcomes.

One- and two-dimensional laser induced fluorescence at oblique incidence

“…However, development of techniques for the analysis of LIF data obtained by laser injection at oblique angles relative to the direction of flow or to the magnetic field in magnetized plasmas is limited [17,[24][25][26][27][28][29]. Historically, researchers have gone to considerable effort to ensure that the laser light is injected either perfectly parallel or perfectly perpendicular to the ambient magnetic field [30,31]; even when optical access is severely limited [32].…”

Survey of CO2 Radiation Experimental Data in Relation with Planetary Entry

“…The same would apply for Venus, but for a much higher pressure, even if a launch at high altitude using a balloon could be envisaged. For such objective, CO 2 expansion flows have been studied by Mazouffre & Pawelec [12] in an arc-jet operating at low pressure, and both pure CO 2 and CO 2 -N 2 mixture were investigated for flow enthalpy of 9.4 and 6 kJ/kg respectively. The experimental set-up is schematized in Figure 6.…”

“…This is relevant for sample return mission to planets with a CO 2 atmosphere such as Mars or Venus (more particularly to Mars since the ground pressure is low contrary to Venus for which a launch from a balloon could be envisaged). For this objective, activities related to modelling [13], database comparison [11], and experiments [12,[14][15] can be found in the literature. In the following, the emphasis will be given to recent experimental campaigns carried out for CO 2 radiation.…”

“…Another interest of CO 2 radiation for propulsion applications is CO 2 expansion flows [12] in nozzles. This is relevant for sample return mission to planets with a CO 2 atmosphere such as Mars or Venus (more particularly to Mars since the ground pressure is low contrary to Venus for which a launch from a balloon could be envisaged).…”

Experimental transition probabilities and Stark parameters of singly ionized noble gases

“…It has been detected in stellar atmospheres (Bidelman 1962), in the interstellar medium (Cardelli, Savage & Ebbets 1991;Cardelli & Meyer 1997), in the solar wind (Morton 2000) and recently in a white dwarf (Werner et al 2012). Krypton is used as propellant in electric propulsion systems and Kr II spectral lines are used for the characterization of ions' velocity distribution functions by means of laser fluorescence in Hall thrusters (Mazouffre & Pawelec 2009). Transition probabilities data are of fundamental importance in the determination of plasma temperatures from the intensities of the spectral line radiation Fonseca & Campos (1982) and Djeniže, Milosavljević & Dimitrijević (2003) report relative transition probabilities, mostly for transitions in the visible part of the spectrum.…”