A parametric AC loss model of the ITER coils for control optimization

A recent study on AC loss calculation in different operating regimes of relevance for ITER plasma control has shown that AC loss calculations can be performed on a model with a level of complexity and completeness not achieved so far [L. Bottura, P. Bruzzone, J.B. Lister, C. Marinucci, A. Portone, Computation of AC losses in the ITER magnets during fast field transients, IEEE Trans. Appl. Supercond. 17 (2) (2007) 2438-2441]. The model developed is however too large and computationally expensive for the inclusion in a fast control optimization procedure. For this reason a second study was launched aiming at developing a simplified calculation method. The simplified calculation method described here that provides faster estimates of AC loss in the ITER coils. The method is based on a Fourier decomposition of the field excitation, calculation for each Fourier component, and sum over all frequencies to estimate the total loss associated with a given current waveform. Typical accuracy that can be reached is of the order of ±30% with respect to a more complete numerical simulation of a single Fourier component, and +60% on the recomposed signal. In spite of the modest accuracy, the advantage is the estimation method respects the scaling of the results of AC loss with amplitude and frequency, and is thus appropriate for optimization studies. Furthermore, the calculation is fully analytical, it is sufficiently fast to be included in the optimization loop of the plasma position and shape control system.