Application of thin foils in low-energy neutral-atom detection

Magnetospheric imaging has been proposed using remote detection of low energy neutral atoms (LENAs) of magnetospheric origin. In the detector, LENAs can be removed from the immense ambient UV by charge state modification (ionization) using a carbon stripping foil and can be subsequently deflected into an E/q analysis section. The LENA detector efficiency is linearly proportional to the ionization probability of neutrals as they transit the foil. In this study, we present equilibrium charge state and scatter distributions for 1 - 30 keV atomic hydrogen and oxygen transiting nominal 0.5 μg cm^-2 carbon foils. The fraction of hydrogen exiting a foil as H⁺ ranges from approximately 5% at 1 keV to 41% at 30 keV. The fraction of oxygen exiting the foil as O⁺ ranges from approximately 2% at 10 keV to 8% at 30 keV. Results obtained after coating the exit surface of foils with either aluminum (which forms aluminum oxide when exposed to air) or gold suggest that the intended alteration of the exit surface chemistry has no effect on the charge state distributions due to foil contamination from exposure to air. Scattering that results from the projectile-foil interaction is shown to be independent of the charge state distribution, illustrating the distinctly different interaction mechanisms associated with charge exchange and scattering.