  Particle acceleration in stellar flares is ubiquitous in the Universe,
however, our Sun is the only astrophysical object where energetic particles and
their source flares can both be observed. The acceleration mechanism in solar
flares, tremendously enhancing (up to a factor of ten thousand) rare elements
like 3He and ultra-heavy nuclei, has been puzzling for almost 50 years. Here we
present some of the most intense 3He- and Fe-rich solar energetic particle
events ever reported. The events were accompanied by non-relativistic electron
events and type III radio bursts. The corresponding high-resolution,
extreme-ultraviolet imaging observations have revealed for the first time a
helical structure in the source flare with a jet-like shape. The helical jets
originated in relatively small, compact active regions, located at the coronal
hole boundary. A mini-filament at the base of the jet appears to trigger these
events. The events were observed with the two Solar Terrestrial Relations
Observatories STEREO on the backside of the Sun, during the period of increased
solar activity in 2014. The helical jets may be a distinct feature of these
intense events that is related to the production of high 3He and Fe
enrichments.
