Solar energetic particles, or SEPs, from suprathermal (few keV) up to relativistic (\(\sim \)few GeV) energies are accelerated near the Sun in at least two ways: (1) by magnetic reconnection-driven processes during solar flares resulting in impulsive SEPs, and (2) at fast coronal-mass-ejection-driven shock waves that produce large gradual SEP events. Large gradual SEP events are of particular interest because the accompanying high-energy (\({>}10\)s MeV) protons pose serious radiation threats to human explorers living and working beyond low-Earth orbit and to technological assets such as communications and scientific satellites in space. However, a complete understanding of these large SEP events has eluded us primarily because their properties, as observed in Earth orbit, are smeared due to mixing and contributions from many important physical effects. This paper provides a comprehensive review of the current state of knowledge of these important phenomena, and summarizes some of the key questions that will be addressed by two upcoming missions—NASA’s Solar Probe Plus and ESA’s Solar Orbiter. Both of these missions are designed to directly and repeatedly sample the near-Sun environments where interplanetary scattering and transport effects are significantly reduced, allowing us to discriminate between different acceleration sites and mechanisms and to isolate the contributions of numerous physical processes occurring during large SEP events.

太阳高能粒子（SEP），从超热（几 keV）到相对论（ \(\sim \)几 GeV）能量在太阳附近至少以两种方式加速：（1）通过太阳耀斑期间磁重联驱动的过程导致脉冲 SEP，以及（2）快速日冕物质抛射驱动的冲击波，产生大的渐进 SEP 事件。大型渐进 SEP 事件特别令人感兴趣，因为伴随的高能（ \({>}10\) s MeV）质子对在近地轨道以外生活和工作的人类探险家以及通信等技术资产构成严重的辐射威胁和太空中的科学卫星。然而，我们无法完全了解这些大型 SEP 事件，主要是因为在地球轨道上观察到的这些事件的特性由于混合和许多重要物理效应的影响而被模糊。本文对这些重要现象的了解现状进行了全面回顾，并总结了即将由美国宇航局的太阳探测器 Plus 和欧空局的太阳轨道飞行器这两个即将执行的任务将解决的一些关键问题。这两项任务的目的都是直接、重复地对近太阳环境进行采样，在这些环境中，行星际散射和传输效应显着减少，使我们能够区分不同的加速地点和机制，并隔离大型 SEP 事件期间发生的众多物理过程的贡献。 。