Tandem-Mirror Architecture

The burner confines plasma along a straight axis between two high-field end plugs, using electrostatic potentials rather than closed field lines.

A linear confinement machine

A tandem mirror is an open, linear device. Plasma sits in a long, weak-field central cell and is capped at each end by a high-field plug. Unlike a tokamak, there are no closed nested flux surfaces and no toroidal plasma current to disrupt. Confinement along the axis is provided by two effects working together: magnetic mirroring and an electrostatic potential built by the plugs.

Why two plugs (tandem)

A single magnetic mirror leaks ions through its loss cone too quickly to burn. The tandem idea, developed in the 1970s, adds a second effect: dense, hot plasma in each end plug raises the local electrostatic potential, producing an ambipolar potential that electrostatically plugs the ends of the central cell for ions. The central-cell ions are then confined by a potential well, not by field-line closure.

Radial confinement is provided by the magnetic field itself — ions and electrons gyrate tightly around field lines. Axial confinement is the hard problem a mirror must solve, and the tandem architecture is the answer the burner uses: a mirror ratio at the throats plus the plug potential.

Consequences of going linear

• No disruptions: no large toroidal current to terminate violently
• Simple maintenance geometry: components lie along a straight line with open ends
• Natural exhaust: escaping plasma streams into an expander and onto a direct converter
• MHD stability must be engineered deliberately — see minimum-B stability

The linear form is also what makes the machine modular and site-friendly: it is a long cylinder with well-defined ends, straightforward to shield, service, and replicate as units.