  Solar prominences are long-lived cool and dense plasma curtains in the hot
and rarefied outer solar atmosphere or corona. The physical mechanism
responsible for their formation and especially for their internal plasma
circulation has been uncertain for decades. The observed ubiquitous down flows
in quiescent prominences are difficult to interpret as plasma with high
conductivity seems to move across horizontal magnetic field lines. Here we
present three-dimensional numerical simulations of prominence formation and
evolution in an elongated magnetic flux rope as a result of in-situ plasma
condensations fueled by continuous plasma evaporation from the solar
chromosphere. The prominence is born and maintained in a fragmented, highly
dynamic state with continuous reappearance of multiple blobs and thread
structures that move mainly downward dragging along mass-loaded field lines.
The prominence plasma circulation is characterized by the dynamic balance
between the drainage of prominence plasma back to the chromosphere and the
formation of prominence plasma via continuous condensation. Plasma evaporates
from the chromosphere, condenses into the prominence in the corona, and drains
back to the chromosphere, establishing a stable chromosphere-corona plasma
cycle. Synthetic images of the modeled prominence with the Solar Dynamics
Observatory Atmospheric Imaging Assembly closely resemble actual observations,
with many dynamical threads underlying an elliptical coronal cavity.
