Vertical stabilisation of Tokamak plasmas

The design of a controller which will control the current in the active control coils of a tokamak fusion reactor is discussed. At this stage, the task is to stabilize and control the vertical position of the plasma. As the linearized models of the plasma dynamics are of very high order, any control system design work must be preceded by a model reduction phase. Model reduction methods based on truncated balancing are used. The control systems are designed using H^∞-based methods. The initial study described indicates that the infinite element models which describe the plasma's vertical dynamics are essential low order. The Krylov subspace method of finding approximate solutions to the gramian equations worked well in this application, and the subsequent model reduction steps were computationally manageable. The H^∞ method for designing controllers worked well, and the closed-loop performance seems relatively insensitive to changes of operating point.