  As one of the most spectacular energy release events in the solar system,
solar flares are generally powered by magnetic reconnection in the solar
corona. As a result of the re-arrangement of magnetic field topology after the
reconnection process, a series of new loop-like magnetic structures are often
formed and are known as flare loops. A hot diffuse region, consisting of around
5-10 MK plasma, is also observed above the loops and is called a supra-arcade
fan. Often, dark, tadpole-like structures are seen to descend through the
bright supra-arcade fans. It remains unclear what role these so-called
supra-arcade downflows (SADs) play in heating the flaring coronal plasma. Here
we show a unique flare observation, where many SADs collide with the flare
loops and strongly heat the loops to a temperature of 10-20 MK. Several of
these interactions generate clear signatures of quasi-periodic enhancement in
the full-Sun-integrated soft X-ray emission, providing an alternative
interpretation for quasi-periodic pulsations that are commonly observed during
solar and stellar flares.
