Separatrix

A separatrix is a boundary between domains with distinct dynamical behaviour (phase curves) in a dynamical system.

In the fusion context, the term refers to the trajectories of the magnetic field lines and is used to describe:

• The boundary between closed and open field lines, separating the toroidally confined region from the region where field lines connect to material surfaces (such as divertors, limiters, or walls) - also known as the Scrape-Off Layer (SOL). This boundary is also called the Last Closed Flux Surface (LCFS).
• The boundary between the inside of a magnetic island and the surrounding region.

See also

• Flux surface