Thomson Scattering Studies in He and He/H2 Nanosecond Pulse Nonequilibrium Plasmas

Abstract

Thomson scattering and kinetic modeling are used to study time evolution of electron density and electron temperature in a nanosecond pulse, diffuse filament electric discharge sustained between two spherical electrodes and operated at a low pulse repetition rate. The experiments have been done for three representative cases: (1) Helium, P=200 torr, discharge pulse energy 17 mJ/pulse; (2) Helium, P=100 torr, discharge pulse energy 0.6 mJ/pulse; and (3) 1% hydrogen in helium, P=100 torr, discharge pulse energy 0.8 mJ/pulse. In Case 1, peak electron number density and peak electron temperature are ne ≈ 3.5·10 15 cm -3 and Te ≈ 4 eV, respectively. The kinetic model predictions agree well with the temporal trends detected in the experiment (rapid initial rise of electron temperature and electron density during the discharge pulse and gradual decay in the afterglow), although peak electron temperature and electron density values during the pulse are somewhat overpredicted. Similar temporal trends, although at lower peak ne and Te, are observed at lower discharge pulse energies. The electron number density decay in a 1% H2 – He mixture is found to be much faster, by approximately a factor of 4, compared to helium at the same pressure and nearly the same discharge pulse energy. This is likely due to more rapid dissociative recombination of electrons in collisions with H2 + ions compared to dissociation recombination of electrons with He2 + ions. At these lower pulse energies, model predictions reproduce temporal trends fairly well, but overpredict peak electron density as well as the rate of electron cooling. D ow nl oa de d by I go r A da m ov ic h on F eb ru ar y 2, 2 01 4 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 413 58 52nd Aerospace Sciences Meeting 13-17 January 2014, National Harbor, Maryland AIAA 2014-1358 Copyright © 2014 by Andrew Roettgen. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. AIAA SciTech