This schematic diagram illustrates the two acceleration sites of ions in large solar energetic particle (SEP) events: flares and CME-driven shocks. Once produced, energetic ions can propagate along open interplanetary magnetic field (IMF) lines and be detected in-situ at 1 astronomical unit, or 150 million kilometers. The density of solar atmosphere near the acceleration sites is high enough so that energetic ions can lead to the production of solar ENAs.