Since the discharge current flows to balance the charge across the capacitor bank, there are a lot of electrons flowing through the circuit to make this happen. These electrons flow through the wires and cables connecting everything together, and then flow through the plasma from the cathode to the anode. Within the volume between the cathode and anode, these electrons are highly mobile and carry the bulk of the current through the plasma.  When ions are accelerated by plasma processes through this volume, they will collect some electrons and draw them onwards to neutralise the plasma exhaust; the ions lose a little bit of momentum as they do this, but due to the large difference in mass between ions and electrons, the momentum loss is negligible.
Other technologies require the complexity of a neutraliser cathode to ensure that the exhaust is neutralised, otherwise a range of bad things can happen.  Our system is self-neutralising, which reduces complexity and increases robustness.