  We demonstrate that particles are regularly accelerated while experiencing
curvature drift in flows driven by magnetic tension. Some examples of such
flows include spontaneous turbulent reconnection and decaying
magnetohydrodynamic (MHD) turbulence, where magnetic field relaxes to a
lower-energy configuration and transfers part of its energy to kinetic motions.
The opposite process, such as dynamo, will actually result in the net cooling
of particles by the curvature drift. Being very generic, this acceleration
mechanism is likely to be responsible in production of non-thermal particle
distribution in magnetically-dominant environments such as solar chromosphere,
pulsar magnetosphere, jets from supermassive black holes, $\gamma$-ray bursts,
etc.
