Ion-Collision Emission Excitation Cross Sections for Xenon Electric Thruster Plasmas

Energetic xenon ion collisions with neutral atoms play an important role in electric thruster plasma radiation at low electron temperatures. The respective emission excitation cross sections are necessary for the derivation of plasma parameters from the observed radiance. We present apparent emission excitation cross sections for near-infrared 5p(exp 5)6p to 5p(exp 5)6s transitions of neutral xenon impacted by singly and doubly charged xenon ions. The cross sections were measured over a laboratory energy-per-charge-number range of 100 to 900 eV, a range that covers typical Hall effect thruster discharge voltages. The cross sections are derived from ion beam luminescence spectra produced at single-collision conditions and at pressures for which radiation trapping effects were shown to be negligible. The Xe(exp 2+) cross sections are significantly higher than those of Xe2+ and increase with energy throughout the investigated range. The Xe(exp 2+) cross sections plateau at approximately 600 eV. The cross sections are incorporated in a collisional-radiative model. The calculations of near-infrared spectra demonstrate that the sensitivity of the model diagnostic with respect to electron temperature increases with ion energy.