Magnetic Control Strategies for the Breakdown and Early Ramp-up in Large Tokamaks

Magnetic control for plasma initiation in a toka-mak is mainly achieved with a feedforward voltage control action pre-computed on the basis of a model of the plant. In medium/large tokamaks, plasma breakdown is dominated by eddy currents induced in the passive structures producing a stray field perturbation to be compensated. There are two main ways to counteract uncertainties in the model used for the design: to iteratively correct the feedfoward control action on the basis of the field reconstructed offline after experiments and/or to adopt a feedback control of the vacuum fields estimated on line. This paper describes methodologies and tools to implement magnetic control strategies including optimization of the feedfoward action, reconstruction of the field map in the plasma chamber, fast feedforward corrections, and feedback control of radial and vertical fields. A collection of numerical simulations on ITER, DEMO and JT60-SA are illustrated.