  A study of the dynamics of the positive charges in liquid argon has been
carried out in the context of the future massive time projection chambers
proposed for dark matter and neutrino physics. Given their small mobility
coefficient in liquid argon, the ions spend a considerably longer time in the
active volume with respect to the electrons. The positive charge density can be
additionally increased by the injection, in the liquid volume, of the ions
produced by the electron multiplying devices located in gas argon. The impact
of the ion current on the uniformity of the field has been evaluated as well as
the probability of the charge signal quenching due to the electron-ion
recombination along the drift. The study results show some potential concerns
for massive detectors with drift of many meters operated on surface.
