Central-Cell Solenoid

The central-cell solenoid is the low-field magnet set that shapes the long burn volume between the two mirror throats.

The central-cell magnets are a set of solenoidal coils that produce a uniform axial field over the burn length. Their job is geometric: keep the field straight and steady so the plasma column is well defined between the throats. They operate at a far lower field than the plugs, which relaxes their structural and cryogenic demands relative to the high-field end coils.

Uniformity matters more than peak field here. Ripple or curvature in the central-cell field can drive particle drifts and degrade confinement, so the coil spacing and current are set to flatten the on-axis profile. The transition into the 17 T throats at each end is shaped by dedicated coils so the mirror geometry is smooth.

Design considerations

• Axial field uniformity across the burn length
• Smooth transition into the 17 T throat regions
• Support against axial magnetic forces pulling coils together
• Cryogenic cooling of the superconducting winding
• Access gaps for fuel, heating, diagnostics, and pumping

Relation to the plugs

The central-cell coils and the plug coils form one magnetic circuit along the axis; their forces are coupled. The strong end plugs pull axially on the whole assembly, and the central-cell spine must carry those loads without distorting the field it is trying to keep uniform. This is a structural-magnetic coupling problem rather than a plasma-physics one, and it is addressed in the machine structural-support page.

Figures are design-and-simulation values for an unbuilt machine.