IBEX-lo on the Interstellar Boundary Explorer (IBEX) will image energetic neutral H atoms (ENA) from the termination shock at 10 – 2000 eV and the flow distribution of interstellar O in spring and fall. The sensor combines a mechanical collimator to restrict the detectable arrival directions, an atom to negative ion conversion surface, an electrostatic analyzer, post-acceleration up to 20 keV, and time-of-flight (TOF) analysis, providing species separation and effective background suppression. Because the flux of the heliospheric ENAs is very low a triple coincidence system is used with secondary electrons produced at two consecutive carbon foils, followed by detection of the ions in a micro-channelplate. These signals are combined into three independent TOF measurements. Meanwhile the flight model of the TOF subsystem has been fabricated, tested and calibrated. It will be shown how the combination of several TOF measurements is very effective to suppress background to unprecedented levels and to identify minor species, whose fluxes are several orders of magnitude below the main species. Results from the testing of both the engineering and the flight unit will be discussed in the light of the IBEX science objectives to study the termination shock and the heliosheath.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 841-844