Helium Ash

The helium produced by fusion, which must be exhausted before it chokes the reaction.

Fusion produces helium, which accumulates as 'ash'. If not exhausted through the divertor it dilutes the fuel and cools the plasma. Ash removal is a core function of the divertor and pumping systems.

Helium ash is fusion's exhaust: the helium produced must be pumped out before it dilutes the fuel and cools the plasma. Ash removal ties core physics to the divertor and vacuum systems, and its efficiency sets a practical ceiling on sustainable fusion power — one reason the divertor and cryopumps are performance-critical, not merely protective.