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.
Common questions
It is the balance where the plasma's outward pressure is held by the magnetic field's inward force, giving a stable shape and position. The control system holds this equilibrium continuously.
Magnetic sensors reconstruct the plasma's position and shape, and the poloidal-field coils are driven to correct it within milliseconds — the core of vertical and shape control.