A Composition Analysis Tool for the Solar Wind Around Pluto (SWAP) Instrument on New Horizons.

We describe the response of the Solar Wind Around Pluto (SWAP) instrument (McComas et al. in Space Sci. Rev. 140:261, ) to 1-40 amu ions in order to assess whether it can be used to determine plasma composition. Our goal is to enhance the scientific return on the SWAP plasma measurements obtained during the New Horizons traversal down Jupiter's magnetotail in 2007. We present calibration data for the SWAP flight instrument and another largely flight-like SWAP sensor, dubbed 'SWAP-II'. SWAP's mass-dependent response was characterized by analyzing the count ratios from its two channel electron multipliers (CEMs). We observe significant differences in the instrument response between light (mass ≤ He) and heavy (mass > He) ions, especially for energies below ∼4 keV. We attribute these differences to the mass-dependent electron emission yield from SWAP's ultra-thin (∼1 μg/cm) carbon foil. Using these results, we develop a plasma composition analysis technique to statistically distinguish between light and heavy plasma ions measured by the instrument. [ABSTRACT FROM AUTHOR]