Topping & Bottoming Stages in the Train

Arranging converters so each takes energy at its own quality level, and passes the remainder down, is how the train beats any single stage.

Cascading by energy quality

A combined-cycle power plant puts a gas turbine on top and a steam turbine below, so the high-temperature exhaust of the first becomes the input of the second. The DEC train uses the same idea with non-thermal converters: each stage sits at the energy quality it handles best, and hands its leftover down the cascade. High-energy ordered beams go to the top; degraded heat goes to the bottom.

Topping versus bottoming

• Topping stages (TWDEC, MHD) take the highest-grade energy first — ordered kinetic energy of ions and flow.
• Bottoming stages (thermionic, radiation recovery) take what has degraded to heat, extracting a last slice before cooling.
• The residual after the bottoming stage is the only part that must be rejected as waste heat.

Why the sum beats the parts

Each stage alone is limited: TWDEC cannot fully decelerate a broad spectrum, MHD cannot convert cold flow, thermionics cannot beat space charge. But because each passes its remainder to a converter suited to that remainder, the system recovers a larger fraction than any single device. The train's design goal is to make the final rejected-heat slice as thin as possible.

The payoff

A thin rejected-heat slice is exactly what lets MetroVolt run with almost no water: the cooling duty is proportional to that residual, not to the whole power output as in a thermal plant. Cascading converters is therefore not only an efficiency strategy but the mechanism behind the burner's siting advantage near data centers and cities.