Pauli Exclusion Principle
From quantum rules, electrons don’t like to be packed into a small
space, either in atoms or in ionized gas
At normal ionized gas densities, electrons are so spread out
quantum rules don’t matter.
As high enough ionized gas densities, quantum rules need to be
considered, just has they have been in atoms
Think of each “atom sized” region of space having a set of energy
levels associated with it  (although it is really more complicated)