Safety Factor (q)

A measure of magnetic field-line pitch that governs large-scale plasma stability.

The safety factor q counts how many times a magnetic field line travels the long way around the torus for each time it goes the short way. It is central to stability: low-order rational values of q are where dangerous MHD modes can grow.

HYPERION targets q₉₅ = 3.0 at the plasma edge, a standard, conservative value that keeps the current profile away from the most disruptive resonances.

The safety factor ties directly to stability limits: the external kink is avoided by keeping the edge q above about 2, and rational surfaces where q is a simple fraction are where tearing modes grow. HYPERION's q₉₅ = 3.0 is a deliberately conservative choice that keeps the current profile clear of the most disruptive resonances.