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We have measured yields of electrons emitted in the forward and backward directions from ultrathin carbon foils due to 10-100 keV atomic and molecular projectiles. In general, electron yields are higher in the forward than in the backward direction. Their behavior with projectile type and energy can be explained by a competition of a forward peaked angular distribution of initial ionization events and elastic collisions that tend to randomize electron motion in the foil. Experiments with ions with atomic number Zϭ1-10 indicate that heavy projectiles produce less electron emission per amount of deposited energy by the projectile near the surface. This is attributed to a larger fraction of low-energy electrons produced by heavy projectiles in the primary ionization event that cannot surmount the surface barrier. For incident molecules, the backward electron yield is less than the sum of the yields of the constituent atoms. Neutral atoms with relatively low ionization potentials produce higher electron yields in the backward direction than the ions of the same species for incident energies above about 5 keV/amu, which is attributed to electron loss from the projectile.

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Over the past several decades, a number of groups have successfully developed and flown space instruments based on ultrathin (0.5–3.5 μg cm−2 or ∼2–17 nm nominal thickness) carbon foils suspended on fine metallic grids. These foils have proven to be remarkably robust in surviving the rigors of the launch and space environments and have functioned as required over long mission lifetimes. This study examines the scientific basis of possible failure mechanisms and the actual flight histories of ultrathin carbon foils. In all, we were able to document 138 separate foils used in 17 independent space instruments on 16 different spacecraft with a cumulative functioning flight history of 93 foil-years in space. All of these foils clearly survived their launches, and there is no evidence for any significant degradation over their various flight histories. This successful flight heritage, combined with laboratory data on foil survivability, shows that properly implemented ultrathin carbon foils are a mature and reliable technology for space flight applications.

Abstract. Initial ENA images obtained with the MENA imager on the IMAGE observatory show that ENAs emanating from Earth's magnetosphere at least crudely track both Dst and Kp. Images obtained during the storm of August 12, 2000, clearly show strong ring current asymmetry during storm main phase and early recovery phase, and a high degree of symmetry during the late recovery phase. Thus, these images establish the existence of both partial and complete ring currents during the same storm. Further, they suggest that ring current loss through the day side magnetopause dominates other loss processes during storm main phase and early recovery phase.