Ultrathin foils used for low-energy neutral atom imaging of the terrestrial magnetosphere

Abstract

Magnetospheric imaging by remote detection of low-energy neutral atoms (LENA5) that are created by charge exchange between magnetospheric plasma ions and neutral geocoronal atoms has been proposed as a method to provide global information of magnetospheric dynamics. For LENA detection, carbon foils can be implemented to (1) ionize the LENAs and electrostatically remove them from the large background of solar UV scattered by the geocorona to which LENA detectors (e.g. , microchannel plates) are sensitive and (2) generate secondary electrons to provide coincidence and/or LENA trajectory information. Quantification of LENA-foil interactions are crucial in defining LENA imager performance. We present equilibrium charge state and angular scatter distributions for 1- to 30-keV atomic hydrogen, helium, and oxygen transiting nominal 0.5 μg cm2 carbon foils. Results obtained after coating the exit surface of foils with either aluminum 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. Angular scattering that results from the projectile-foil interaction is quantified and is shown to be independent of the charge state distribution.