Tandem-Mirror Equilibrium for the Burner

Modeling the burner's open-ended magnetic geometry, end-plug fields, and ambipolar potential that confine a D-3He plasma.

A different confinement problem

The burner is not a tokamak; it is a D-3He tandem-mirror generator with an open-ended magnetic geometry. Its equilibrium problem is not Grad-Shafranov but the balance of an axial magnetic mirror plus electrostatic confinement. L0 models this geometry to establish how the central cell is confined by the high-field end plugs at 26.49 T with a 17 T throat.

The ambipolar potential

Confinement in a tandem mirror depends on the ambipolar potential: end plugs are held at higher density to raise an electrostatic potential that plugs the ends against ion loss. Modeling this couples the magnetic field structure to the plasma potential and density along the axis, a self-consistent problem the burner solves on L0 across plug and central-cell conditions.

• Axial magnetic field profile: 26.49 T plug, 17 T throat, central cell
• Ambipolar potential barrier from plug density
• Central-cell density and temperature confinement scaling
• Mirror-ratio and end-loss balance

Stability of the open system

Open systems are prone to interchange and flute modes driven by unfavorable field-line curvature. The burner MHD workloads test whether the configuration is stable and what shaping or profile control keeps it so. These solves are the burner's analogue of the breeder's disruption studies: they establish the operating envelope the control system must hold.

The equilibrium and potential solves generate the training data for the burner's twin modules, the ambipolar-potential surrogate and end-plug density estimators that must run in real time. As with the breeder, expensive self-consistent physics is computed once offline so the twin can evaluate it cheaply during operation.

This work also feeds the direct-energy-conversion design. The end-loss ion distribution that the mirror deliberately allows to escape is exactly what the DEC train, TWDEC, ultra-high-field MHD, and thermionics, harvests, so the equilibrium model is coupled to the conversion physics from the start.