kink instability is a current-driven plasma instability that bends the entire plasma column into a growing helical corkscrew, like a twisted rope buckling under torsion.
The kink is one of the oldest instabilities in fusion research, familiar from the earliest pinch experiments of the 1950s: drive enough current through a column of 📝plasma and the column refuses to stay straight, because any slight bend concentrates the magnetic field on the inside of the bend and amplifies it. It is an ideal magnetohydrodynamic instability — it requires no electrical resistance to grow, which makes it fast and violent, developing on microsecond timescales. That places it in contrast with its resistive cousin, the 📝tearing mode, which grows slowly by reconnecting field lines rather than displacing the whole column.
Taming the kink is the founding logic of the 📝Tokamak: a strong 📝toroidal field stiffens the plasma column against bending, and stability requires the 📝safety factor (q) to stay above 1 — the Kruskal-Shafranov condition, which caps how much 📝plasma current a machine of given field and size can carry. The external kink, in which the plasma boundary itself deforms, sets hard operational limits; the internal kink, confined inside the q = 1 surface, drives the 📝sawtooth oscillation seen in nearly every tokamak core.