Ambipolar Potential
An electrostatic potential in a tandem mirror that plugs ion end-losses.
In a tandem mirror, dense high-field plugs at each end build up an electrostatic potential that repels ions trying to escape from the central cell — an 'ambipolar' plug that confines ions electrostatically rather than only magnetically.
Establishing this potential requires the plug to reach a density well above the central cell — the burner's plug-density requirement of about np/nc = 16.
The ambipolar potential is the mechanism that makes a modern tandem mirror viable: dense end plugs build an electrostatic barrier that confines central-cell ions where magnetism alone cannot. Its depth scales with the plug-to-central density ratio, which is why the Kronos burner's net power depends on reaching a ratio near 16.