  Pure carbon clusters have received considerable attention for a long time.
However, fundamental questions such as what the smallest stable carbon cluster
dication is remain unclear. Here, we investigated the stability and
fragmentation behavior of C_n^{2+} (n=2-4) dications using state-of-the-art
atom probe tomography. These small doubly charged carbon cluster ions were
produced by laser-pulsed field evaporation from a tungsten carbide field
emitter. Correlation analysis of the fragments detected in coincidence reveals
that they only decay to C_{n-1}^+ + C^+. During C_2^{2+} => C^+ + C^+,
significant kinetic energy release (\approx 5.75-7.8 eV) is evidenced. Through
advanced experimental data processing combined with \textit{ab initio}
calculations and simulations, we show that the field evaporated diatomic
^12C_2^{2+} dications are either in a weakly bound ^3{\Pi}_u and ^3{\Sigma}_g^-
state, quickly dissociating under the intense electric field, or in a deeply
bound electronic ^5{\Sigma}_u^- state with lifetimes longer than 180 ps.
