Helium Ash Transport

How fusion-produced helium moves and must be exhausted.

Goal

Exhaust ash, avoid dilution

Helium 'ash' from fusion must be transported to the edge and pumped out before it dilutes the fuel. Helium transport and exhaust efficiency set a limit on sustainable fusion power, tying core physics to the pumping system.

It is one reason the divertor and vacuum pumping are performance-critical, not just protective.