Presentation #411.01 in the session High-energy Solar Investigations through Next-generation Remote Sensing: Spectroscopy, Imaging, and Beyond II.
Observations of the acceleration and transport of ions in solar flares, coronal mass ejections (CMEs), and their combination — solar eruptive events — are critical to understanding the transient, efficient release at the Sun of stored magnetic energy. Up to tens of percent of the energy released in solar flares goes into accelerating ions up to tens of GeV and electrons up to hunderds of MeV, but ion-associated signatures are significantly more challenging to observe than electron-associated signatures. Measuring ion acceleration is important not only for comprehensive understanding of the underlying physical processes, but also for understanding the origin of solar energetic particles (SEPs). Intriguing observations by RHESSI and by Fermi/LAT have shown that there is still much to learn. Remote observations of accelerated ions are traditionally made through gamma rays, and two upcoming missions will make next-generation observations at MeV energies: the GRIPS balloon mission will image gamma-ray sources with unprecedented angular resolution, and the COSI astrophysics SMEX mission will measure faint gamma-ray lines with unprecedented sensitivity. In addition to gamma rays, accelerated ions will also produce energetic neutral atoms (ENAs), and there are multiple instrument concepts under development with the express objective to observe, and even image, solar ENAs. A long-term goal would be a flagship-level mission (e.g., the COMPLETE concept) that coordinates both gamma-ray and ENA measurements with next-generation measurements at other wavelengths.