Residual Heat In A Burner

The burner is not heatless: neutron energy, converter losses, and magnet losses produce residual heat that must be cooled, but the total is small and dry-rejectable.

Where residual heat comes from

• Neutrons: 5.44% of fusion power is carried by neutrons that deposit energy in the surrounding structure
• Direct-converter losses: imperfect deceleration and collection shed some energy as heat
• Magnet and cryogenic losses: sustaining the 26.49 T plug and 17 T throat carries a refrigeration load
• Plasma-facing surfaces: heat and particle flux to the first wall and end regions

These are real loads that a working burner must remove. The point of the water story is not that they vanish, but that together they are a small fraction of a steam plant's rejected heat, and small loads are easy to reject to air.

Why the residual does not bring back the water problem

A steam plant is forced to use wet cooling because its rejected heat is enormous and dry cooling would tax its whole output. The burner's residual is small, so dry cooling imposes only a small penalty. Closed coolant loops carry the heat to air-cooled exchangers, consuming essentially no water in the process.

Honest framing

The exact split among these residual sources depends on the final engineering, which is still in simulation. What is robust is the direction: eliminating the steam cycle removes the dominant heat-rejection load, leaving residuals that closed-loop, dry, near-zero-water cooling can handle.