The Expander Tank
Beyond each plug the field fans out into a large tank, spreading the escaping plasma over a wide area before it reaches the converter.
Fanning out the exhaust
Plasma that leaks past the plug streams along field lines into the expander — a large vacuum tank where the magnetic field drops rapidly and the flux tube expands. As the field falls, the flux tube widens by the ratio of high field to low field, so the power that concentrated in a small throat cross-section spreads across a broad end wall.
Why spread the plasma
- Reduces heat flux on plasma-facing surfaces to manageable levels
- Converts perpendicular ion energy back to parallel as the field drops
- Prepares a broad, directed particle stream for direct conversion
- Separates electrons and ions spatially for collection
Field-line physics
In the expander the same magnetic-moment conservation that reflects ions at the throat now works in reverse: as field drops, perpendicular energy converts to parallel energy, so the exhaust becomes a directed beam of ions flowing away from the machine. That directionality is exactly what a direct converter needs — it collects ordered kinetic energy, not random thermal motion.
The expander also serves as the machine's main pumping volume, since neutralized exhaust accumulates here. Its size is set by the allowable end-wall heat flux and by the expansion ratio needed to make the converter efficient. The expander is the bridge between the confined burn and the electricity-producing end of the plant.