The same gas can carry electricity in profoundly different ways. Push a little current through a sharp point and you get a corona — a thin shell of ionization hugging the tip. Lower the pressure between two plates and a glow discharge fills the tube with soft, diffuse light. Let the current run away and the channel constricts into a blinding, thermal arc. Add a dielectric barrier and the discharge shatters into thousands of self-quenching filaments — the DBD. Switch between the four and watch where the plasma forms and how it behaves.
The four panels are schematic sketches of discharge character — where ionization sits and whether it is diffuse, filamentary, or constricted — not field-solver output. Real regime boundaries depend on gas, pressure, electrode geometry, and the external circuit; one regime can transition into another as current rises, and the DBD panel shows its common filamentary mode (diffuse barrier discharges also exist). The barrier strongly suppresses arcing in normal operation but is not an absolute guarantee against insulation failure or flashover. Filament flicker and the arc's wander are stylized for visibility.