System-Level Optimization of ITER Magnetic Diagnostics: Preliminary Results

The present accuracy requirements on ITER parameters to be obtained primarily from magnetic measurements are demanding and, in many situations, they might be approached but not necessarily achieved with the parameter estimation process currently foreseen. In such cases, it is desirable to improve the estimation process, where possible, to achieve adequate performance. Where the accuracy requirements are still not achieved, the requirements will need to be qualified. This could mean acceptance of increased errors for conditions not impairing machine performance unacceptably, a reduction in operational space of applicability of accuracy requirements (e.g. for the diamagnetic poloidal beta measurement), separation of acceptable dynamic from static errors (e.g. for plasma-wall gap measurements) and separation of acceptable systematic from random errors (e.g. random errors due to plasma generated noise). Modification of the parameter estimation process could include use of magnetic sensors with increased performance (implying increased development time and cost), optimization of the number and position of the magnetic sensors, partial compensation of pick-up from ferromagnetic materials, estimation and partial compensation of pick-up from eddy currents. The first step of improving the ITER magnetic diagnostic specification is an assessment of the plasma parameter estimation accuracies obtainable with the present design of the system. This paper aims at presenting the analysis results with respect to plasma current, plasma-wall gaps and plasma current centroid vertical velocity. Moreover, preliminary results on the reconstruction of TAE perturbations are presented. Although previous work in this area has been reported, this is the first study combining the complete baseline ITER magnetics diagnostic with a realistic and detailed description of the ITER machine, in 3D