What is the plug-density ratio and why does it matter?

In the tandem-mirror burner, the end plugs must reach a density about 16× that of the central cell to build a deep enough electrostatic potential to confine the central ions. The burner's net-positive operation depends on it, which is why Kronos labels that net power requirement-class.

It is the single most important honest caveat on the burner, and Kronos states it openly.