  Coronal mass ejections (CMEs) and eruptive flares (EFs) are the most
energetic explosions in the solar system. Their underlying origin is the free
energy that builds up slowly in the sheared magnetic field of a filament
channel. We report the first end-to-end numerical simulation of a CME/EF, from
zero-free-energy initial state through filament-channel formation to violent
eruption, driven solely by the magnetic-helicity condensation process. Helicity
is the topological measure of linkages between magnetic flux systems, and is
conserved in the corona, building up inexorably until it is ejected into
interplanetary space. Numerous investigations have demonstrated that helicity
injected by small-scale vortical motions, such as those observed in the
photosphere, undergoes an inverse cascade from small scales to large,
`condensing' at magnetic-polarity boundaries. Our new results verify that this
process forms a filament channel within a compact bipolar region embedded in a
background dipole field, and show for the first time that a fast CME eventually
occurs via the magnetic-breakout mechanism. We further show that the trigger
for explosive eruption is reconnection onset in the flare current sheet that
develops above the polarity inversion line: this reconnection forms flare loops
below the sheet and a CME flux rope above, and initiates high-speed outward
flow of the CME. Our findings have important implications for magnetic
self-organization and explosive behavior in solar and other astrophysical
plasmas, and for understanding and predicting explosive solar activity.
