Plasma Distributions and Composition at the Magnetopause: MMS HPCA observations

Reconnection at the Earth's magnetopause is the mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy, mass and momentum to flow into the magnetosphere. It is the primary science goal of the recently launched MMS mission to unlock the mechanism of magnetic reconnection with a novel suite of plasma and field instruments. A component of the plasma suite is the Hot Plasma Composition Analyzer (HPCA) which provides accurate measurements of the major ion species (H+, He++, He+, O+) present in the near Earth environment. The HPCA instrument employs a RF unit in the ion optics to artificially reduce the proton flux in areas with high proton flux where measurements of minor ion species are usually masked or contaminated by the high proton flux. This presentation will discuss first measurements of ion distributions at the magnetopause by the HPCA instrument.