Burner High-Field Plug Throats
The plug throats are the intense high-field regions at each end that reflect plasma back into the central cell.
The magnetic stoppers
At each end of the central cell the magnetic field is squeezed to a very high value in a short region called the plug throat. A charged particle moving from weak field into strong field is turned around, the magnetic mirror effect, so the throats act as stoppers that reflect central-cell plasma back inward instead of letting it stream out the ends.
The field values
- The plug reaches 26.49 T, the highest field anywhere in either Kronos machine.
- The throat runs at 17 T.
- The ratio between the throat field and the central-cell field, the mirror ratio, sets how well particles are reflected.
Why the field must be so high
Confinement in a mirror improves with the mirror ratio, the jump from central-cell field to peak plug field. A higher peak field turns back a larger fraction of particles, so pushing the plug to 26.49 T directly buys confinement. Reaching that field is why the burner, like Hyperion, depends on high-temperature REBCO superconductor; no conventional magnet reaches it in this geometry.
Tandem plugging
The high field alone is not enough for a fusion-grade device, so the plugs also establish an electrostatic potential that repels central-cell ions. The throat is where the magnetic and electrostatic confinement combine. This is the defining feature of a tandem mirror and the reason the plug region is the most demanding part of the machine.
In the model
The plug throats are selectable at each end of the axis, with the 26.49 T and 17 T callouts attached to the geometry. The axial cutaway shows the field lines pinching through the throat. See the mirror coils that produce the field and the expander beyond the throat.