  We investigate experimentally the plasma dynamics of a centimeter-scale,
laser filamentation-guided spark discharge. Using electrical and optical
diagnostics to study monopolar discharges with varying current pulses we show
that plasma decay is dominated by free electron recombination if the current
decay time is shorter than the recombination characteristic time. In the
opposite case, the plasma electron density closely follows the current
evolution. We demonstrate that this criterion holds true in the case of damped
AC sparks, and that alternative current is the best option to achieve a long
plasma lifetime for a given peak current.
