X-point is the point in a tokamak's cross-section where the poloidal magnetic field vanishes and the separatrix crosses itself in the shape of an X, steering the exhaust plasma into the divertor.
The X-point is manufactured, not found: external shaping coils cancel the 📝poloidal field at a chosen location, usually below the plasma, and the field-line geometry around that null forms the characteristic X. The two legs of the X below the null carry the open field lines of the 📝separatrix down to the 📝divertor targets, so heat and particles leaving the confined 📝plasma travel a prescribed path to surfaces engineered to receive them, well away from the confinement region. A machine with one null is a single-null configuration; adding a second X-point at the top makes it double-null, splitting the exhaust between two divertors.
The X-point is what distinguishes a diverted 📝Tokamak from the older 📝limiter machines, and its consequences reach beyond exhaust plumbing: the magnetic geometry near the null underpins access to 📝H-mode, whose discovery on the diverted ASDEX tokamak in 1982 roughly doubled achievable confinement. Modern variants — the snowflake and Super-X divertors — reshape the field around the X-point to increase 📝flux expansion, spreading the exhaust over more target surface, one of the main levers for taming the heat-flux problem in power-plant-scale machines.