Whitepaper #129 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics.
Understanding accelerated particles at the Sun is one of the most important problems in heliophysics. Flare-accelerated particles have huge energies; are an important source of particles in the heliosphere; and are the most important corollary to other areas of high-energy astrophysics. This paper describes the scientific motivation for X-ray studies of particle acceleration at the Sun.