Helium Ash & Exhaust

Fusion produces helium 'ash' that must be pumped out before it dilutes the fuel. The divertor and pumping system handle it in the Kronos design.

What

Spent helium nuclei left after fusion

Problem

Accumulation dilutes the fuel and cools the plasma

Removal

Exhausted through the divertor and pumped

Related

Direct energy conversion first harvests their energy

Every fusion reaction leaves a product behind — most often a helium nucleus (an alpha particle). Once those alphas have given up their energy, they become helium ash: inert nuclei that, if allowed to build up, dilute the fuel and radiate energy away, throttling the burn. A power plant must continuously remove ash at the same rate it is produced.

In Kronos MetroVolt the ash is swept into the scrape-off layer, carried to the divertor, and pumped out of the vacuum vessel. Crucially, the alphas' kinetic energy is first harvested by the direct-energy converter while they are still fast — so helium is both the fuel's exhaust and, on its way out, a source of the plant's electricity.