magnetics diagnostics are the coil-based measurements of plasma current, position, and shape that form the sensory backbone of real-time control in magnetic confinement devices.
They are the oldest and simplest of plasma diagnostics, built on nothing more exotic than Faraday's law: a loop of wire develops a voltage when the magnetic flux through it changes. What distinguishes them from every other diagnostic family is that they never look at the 📝plasma at all — they read the magnetic fields it produces from outside the 📝vacuum vessel, which makes them rugged, continuous, and immune to the harsh conditions that complicate optical access. A Rogowski coil encircling the plasma measures the total 📝plasma current; flux loops track the loop voltage driving it; a diamagnetic loop reads the plasma's stored energy; and arrays of discrete pickup coils around the vessel wall sample the field at many points.
Those coil signals are the inputs to equilibrium reconstruction, the computation that infers the plasma's boundary, position, and internal current distribution — and they close the feedback loops that hold a shaped plasma in place inside a 📝Tokamak, where vertical position is actively unstable and must be corrected continuously. High-frequency Mirnov coils extend the family into stability monitoring, picking up the rotating magnetic signatures of growing instabilities and providing early warning of an approaching 📝disruption.