Flow dynamics of a pulsed planar expansion

Ludovic Biennier (1) , Abdessamad Benidar (2) , Farid Salama (3)

1 PALMS - Physique des atomes, lasers, molécules et surfaces
2 IPR - Institut de Physique de Rennes
3 ARC - NASA Ames Research Center

Plasma expansion sources are popular in molecular spectroscopy and in astrochemistry because they generate cold radicals and ions in detectable amounts. The dynamics of a planar flow generated by a pulsed discharge slit nozzle (PDN) have been numerically investigated for a variety of carrier gases seeded with various molecular species. The determination of the bulk flow characteristics is key to a comprehensive modeling of the plasma that is produced in PDN sources. It is found that the flow is established and stabilized within 75 and 25 μs when Ar and He are used as carrier gases, respectively. The residence time in the inter-electrode active region is found to be considerably shorter with He than with Ar gas carrier. The detection signal observed upon injection of astrochemical species such as polycylic aromatic hydrocarbons (PAHs) in moderate amounts in the carrier gas exhibits a non linear relation with the initial PAH concentration in the reservoir which is governed by the temperature. The local temperature along the flow axis can be predicted from the initial conditions using the isentropic equation. However, the local pressure and density behavior diverge significantly from an isentropic flow. Finally, implications for the characteristics of the plasma expansion are discussed to help design future laboratory simulations.

Mots clés: Computational flow dynamics; Pulsed planar expansions; Pulsed discharge nozzles; Astrochemistry; Molecular spectroscopy; Polycyclic aromatic hydrocarbons

Ludovic Biennier, Abdessamad Benidar, Farid Salama. Flow dynamics of a pulsed planar expansion. Chemical Physics, 2006, 326 (2-3), pp.445-457. ⟨10.1016/j.chemphys.2006.03.016⟩. ⟨hal-00653467⟩