Xenon charge exchange cross sections for electrostatic thruster models

Charge exchange between xenon ions and xenon atoms is the source of a detrimental low energy plasma in the vicinity of electrostatic spacecraft thrusters. Proper modeling of charge-exchange induced spacecraft interactions requires knowledge of the respective charge-exchange cross sections. Guided-ion beam measurements and semiclassical calculations are presented for xenon atom charge-exchange collisions with Xe+ and Xe2+ at energies per ion charge ranging from 1 to 300 eV. The present measurements for the symmetric Xe++Xe exchange system are in good agreement with several earlier experimental studies and semiclassical calculations based on the most recently computed Xe-2(+) interaction potentials. The cross sections are similar to30% higher than predictions by the Rapp and Francis model [D. Rapp and W. E. Francis, J. Chem. Phys. 37, 2631 (1962)]. The present Xe2++Xe symmetric charge exchange measurements are the first to cover the ion energy range from 40 to 600 eV. The cross sections are in good agreement with low-energy drift tube measurements and are significantly lower than previous higher energy measurements. A simple model for symmetric two-electron transfer is proposed that is in good agreement with the present measurements. The onset for the asymmetric charge-exchange process, Xe2++Xe-->2Xe(+), is observed to be at 10 eV. For this process, a cross section of 2.8+/-0.9 Angstrom(2) is measured for a Xe2+ energy of 600 eV. (C) 2002 American Institute of Physics.