MODEL-REDUCTION FOR AXISYMMETRICAL TOKAMAK CONTROL

The problem of reducing a complicated electromagnetic passive structur e model coupled to a linear plasma response model to a size that allow s rapid calculations of gains for plasma position and shape control is discussed. Model reduction through eigenmode decomposition does not r eproduce the input-to-output relationship of the system unless one has a good idea of which eigenmodes are important. Hankel singular mode d ecomposition, on the other hand, provides an orthogonal basis for the system response, where the modes are ordered by their importance to th e input-to-output relationship. A perturbed equilibrium plasma respons e model is used together with an electromagnetic model of the Alcator C-Mod passive structure to assess the performance of different model r eduction schemes. Between 10 and 20 modes are required to give an adeq uate representation of the passive system. Emphasis is placed on keepi ng the reduction process independent of the parameters of the plasma t o be controlled.