Tandem-Mirror Principle

A tandem mirror uses two high-field end plugs to build electrostatic barriers that confine a long central-cell plasma along an open magnetic axis.

A single magnetic mirror confines charged particles by increasing the field at each end of an open tube. Particles with too little velocity parallel to the axis are reflected, but those inside the loss cone escape. A simple mirror leaks too fast to sustain a burning plasma. The tandem-mirror concept adds a small, dense, high-field plasma at each end whose electrostatic potential plugs the loss cone for the much larger central cell.

In the burner (Aegis / MetroVolt) the plugs sit at 26.49 T and the throats at 17 T. The potential built in the plugs raises an ambipolar barrier that reflects central-cell ions electrostatically, not just magnetically. The central cell can then run at lower field and higher volume while still holding its ions long enough to burn D–³He.

The confinement chain

• Plug field 26.49 T sets the mirror ratio and the plug plasma pressure
• Plug plasma builds an ambipolar potential peak
• That potential reflects central-cell ions along the axis
• Throat at 17 T anchors the mirror geometry between plug and cell
• Central cell burns at lower field, larger volume, steady state

Honest gate

The plug is where the concept is hardest. Holding 26.49 T over the plug bore drives coil stress to roughly 3–3.9x the feasible limit as specified, and the plug plasma regime sits 166–830x beyond any device operated to date, so it cannot be post-dicted from existing data. These are design-and-simulation findings, stated in full on the plug-coil-stress and plug-regime gate pages.

The tandem-mirror principle is decades old in the fusion literature; what the burner adds is the D–³He fuel choice, the field levels, and a DEC train matched to the end loss. The principle is sound; the parameters are the open questions.