Deep Dive: The Vacuum System

A fusion plasma needs an ultra-high vacuum — any stray gas would cool and contaminate it. The vacuum vessel and pumping system maintain and protect that environment.

Requirement

Ultra-high vacuum around the plasma

Why

Stray gas cools and contaminates the plasma

Vessel

First structural + safety boundary

Pumping

Removes exhaust and helium ash

Before a plasma can even form, the chamber must be pumped to an ultra-high vacuum — a near-perfect emptiness. Any residual gas would cool the plasma edge, raise the impurity content (Z_eff), and undermine confinement. Maintaining that vacuum continuously, while fuelling and exhausting the plasma, is a demanding systems job.

The vacuum vessel holds this environment and forms the machine's first structural and safety boundary, sitting between the plasma-facing components and the magnets. The pumping system continuously removes the helium ash and unburned fuel that flow to the divertor, feeding the fuel-recovery loop.

Vacuum integrity, plasma purity, and exhaust all depend on this system — and maintaining it is one reason the demountable magnets matter, since they allow vessel access without dismantling the coils. See fuelling & exhaust.