Quasi-Spherical Magnetic Confinement of a Fusion Plasma

The advantages for fusion in a spherical geometry have been recognized for many decades. The design of such systems pose special challenges for magnetic confinement, as magnetic cusps are inherently introduced at the surface boundaries. The (hexahedron) Polywell is a unique case, configured with six-magnetic coils on each face of a cube, biased to produce a null-magnetic field at the polygon's center. Magnetic confinement of a high-power electron-beam, injected through several of the coils, produced a central, negative-potential well for electrostatic ion confinement. Critics dismissed the concept as an implausible-reactor due to its non-thermal particle distribution, even as experiments demonstrated respectable levels of magnetic beta, β ≈ 45%. PIC code simulations configured for the continuous injection of a DD plasma beam, ultimately scaled to near-unity gain for H-B¹¹. Magnetic cusp particle loss remains an identified constraint, that could potentially be addressed through the use of electrostatically-biased reflectors. Our present studies are investigating higher-order magnetic periodicity, in a dodecahedron, which result in substantially reduced particle losses compared to previous work. This paper provides direct comparisons of the loss rates and power balance for several geometries, indicating that even higher magnetic periodicity may be beneficial. Such an approach may eventually provide for a scalable, naturally formed, high-beta, quasi-spherical confinement, suitable for advanced fuels.