The 17 T Throat Field
At each mirror throat the field reaches 17 T, setting the magnetic pinch that reflects particles before the plug potential acts.
The magnetic pinch
Between the central cell and the plug, the field rises to a 17 T throat. This is the magnetic pinch that provides the first stage of confinement — the mirror reflection — before the electrostatic plug provides the second. The throat field, together with the central-cell field, sets the mirror ratio R = Bthroat/Bcell that determines the loss-cone width.
The throat is also a high-stress magnet region, though less extreme than the 26.49 T plug. It shapes the field lines that funnel plasma from the wide central cell down through the pinch and out toward the expander, and its precise profile matters for both confinement and for the flow of exhaust to the direct converter.
Working with the plug
Magnetic mirroring at the throat and electrostatic plugging at the plug are complementary: the throat sets the loss cone, and the plug potential closes most of what remains. Getting the two fields — 17 T throat and 26.49 T plug — into the right ratio and profile is central to the tandem-mirror confinement scheme.
Because the throat and central-cell fields together fix the mirror ratio, the 17 T value is chosen jointly with the cell field rather than in isolation — a stronger throat narrows the loss cone but adds magnet stress and steepens the field gradient the plasma must follow. It is a deliberate midpoint between confinement and buildability, and less extreme than the plug it feeds.
- Throat field: 17 T at each end
- Provides the magnetic mirror reflection
- Sets mirror ratio and loss-cone width
- Funnels exhaust toward the expander/DEC