There is an option (3D only) to quantise the charges in space-charge tubes.
We define: q = charge in tube, p = charge of a single particle, f = q/p.
When f < 1 the program generates a random number r between 0 and 1. If r < f the program replaces q with p, otherwise q is set to 0.
With this procedure the statistical average of the charges in the low-charge tubes remains unchanged but the individual charges become either the particle charge or 0.