  In this paper, the temporal evolution of 3-dimensional relativistic current
sheets in Poynting-dominated plasma is studied for the first time. Over the
past few decades, a lot of efforts have been conducted on studying the
evolution of current sheets in 2-dimensional space, and concluded that
sufficiently long current sheets always evolves into the so-called
"plasmoid-chain", which provides fast reconnection rate independent of its
resistivity. However, it is suspected that plasmoid-chain can exist only in the
case of 2-dimensional approximation, and would show transition to turbulence in
3-dimensional space.
  We performed 3-dimensional numerical simulation of relativistic current sheet
using resistive relativistic magnetohydrodynamic approximation. The results
showed that the 3-dimensional current sheet evolve not into plasmoid-chain but
turbulence. The resulting reconnection rate is $0.004$ which is much smaller
than that of plasmoid-chain. The energy conversion from magnetic field to
kinetic energy of turbulence is just 0.01\% which is much smaller than typical
non-relativistic cases. Using the energy principle, we also showed that the
plasmoid is always unstable for a displacement in opposite direction to its
acceleration, probably interchange-type instability, and this always results in
seeds of turbulence behind the plasmoids. Finally, the temperature distribution
along the sheet is discussed, and it is found that the sheet is less active
than plasmoid-chain. Our finding can be applied for many high energy
astrophysical phenomena, and can provide a basic model of the general current
sheet in Poynting-dominated plasma.
