A collimator design for monitoring heliospheric energetic neutral atoms at 1 AU Original Research Article

SOHOʹs detection of heliospheric energetic H and He atoms in the energy range ∼55–280 keV has led to simulations of the production of these particles in the heliosheath and inner heliosphere that could be compared with observation. Improved and extended observation of heliospheric energetic neutral atoms (ENA) in this energy range should be useful in at least three related areas of study. These are: (1) the acceleration of pickup ions in the inner heliosphere, then again at the termination shock to become anomalous cosmic rays, and their subsequent propagation in the heliosheath; (2) the anomalous cosmic ray spectrum at the termination shock; and (3) the latitudinal distribution of heliospheric shock structures. Future advances in this field will require a new generation of ENA spectrometers. Essential to all ENA spectrometers is an effective ion-rejecting collimator. Taking advantage of the lessons learned from the first generation of ENA instruments and new computer simulations, we report on a preliminary design for an ion-rejecting collimator suitable for second-generation instrument to monitor ENA of both inner and outer heliospheric origins at the readily accessible L1 location at 1 AU.