Scrape-Off Layer

The thin edge region where field lines lead to the divertor rather than closing on themselves.

Just outside the confined plasma, magnetic field lines are 'open' — they intersect the divertor. This scrape-off layer carries the exhaust heat and particles to the targets, and its width sets how concentrated that load is.

The scrape-off layer is a thin, ferociously-loaded region: its width, often only millimetres, decides how concentrated the divertor heat flux is. Because a narrow layer implies a fierce peak, understanding and widening it — or radiating the power away before it lands — is central to protecting the divertor.