Plasma Equilibrium

The force balance between plasma pressure and magnetic field that holds a steady plasma.

Balance

Pressure vs magnetic force

A confined plasma sits in equilibrium when the outward push of its pressure balances the inward force of the magnetic field everywhere. In a tokamak this balance is described by the Grad–Shafranov equation, whose solutions are the nested flux surfaces. Finding and controlling equilibrium is the starting point of operation.

The equilibrium sets the plasma's shape, and holding it is the job of the poloidal-field control system.