What is a tandem mirror?
A tandem mirror is a linear machine: a long, straight central cell capped at each end by a high-field magnetic plug. It is the architecture Kronos chose for the burner — the machine built in two lengths as Aegis and MetroVolt.
- Class
- Open (linear) magnetic confinement
- Kronos role
- The D–³He burner (Aegis / MetroVolt)
- Central-cell field
- B_m ≈ 17 T · end-plug throat 26.49 T (frozen A11)
- No divertor, no ELMs
- Structural — open field lines (frozen B29)
Unlike a tokamak, which bends its field lines into a closed torus, a mirror machine keeps them open and straight. Plasma is held in a central cell by making the magnetic field stronger at each end — a "magnetic mirror" reflects most particles back toward the middle. On its own, a simple mirror leaks too fast to be a reactor. The tandem mirror fixes this: it adds a high-field plug at each end whose dense plasma raises an electrostatic potential that electrostatically confines the ions of the central cell. The plugs do the confining; the central cell does the burning.
Three consequences make this the right geometry for the Kronos burner:
- No divertor, no ELMs — by architecture, not mitigation. An open system has no X-point, no separatrix, no H-mode pedestal, so the edge-instability and exhaust problems that gate every tokamak are simply absent. Kronos freezes this as a structural property of the machine, not a claimed advantage.
- Exhaust becomes electricity. Particles that stream out the open ends land on direct-energy-conversion collectors, turning end-loss into current instead of heat.
- Length is a free dial. The intensive physics (gain, cleanliness) is set by the plasma conditions; total power scales with how long you make the central cell. That is why one design becomes two products — a 440 m Aegis and a 1400 m MetroVolt.
The counterpart to the tokamak's divertor is the mirror's end expander: the ~906 MW of axial loss must be spread over enough collector area to survive. From the 26.49 T ion-end throat, flux conservation calls for roughly a 53× area expansion (down to ~0.5 T) to reach a divertor-class 3.7 MW/m². Kronos records this as a requirement the design must meet — the mirror's homework, stated plainly.