White noise characterization and thermo-mechanical analysis of DTT pick-up coils

The Divertor Tokamak Test (DTT) [1] is presently in the start-up phase of construction. Among diagnostics, the magnetic ones are the first components that will have to be ready for installation and commissioning when DTT vacuum vessel and magnets will be assembled. In this paper, the white noise characterization of DTT in-vessel pick up coil measurements and the thermo-mechanical analysis of ex-vessel pick up coils will be presented referring to the 2021 probe configuration. In particular, the systematic error due to white noise affecting the 80 internal pick-up coil measurements on plasma position reconstruction has been assessed. Such plasma reconstruction has been done by assuming a filamentary representation of the plasma current density. The effect of noise on the measurements is characterized evaluating the mean error, the mean square error and the standard deviation, on the difference between the noisy inverse reconstruction and the ideal inverse reconstruction evaluated on suitable plasma-wall gaps. Moreover, a feasibility study of mounting a torlon pick-up coil between the vacuum vessel and the thermal shield, in terms of bulk has been developed. In addition, the probe thermomechanical stresses are preliminarily investigated for backing and operative conditions, assuming a welding as mounting solution. The study shows that no bulk criticality is present for mounting the external pick-up coil. The operative temperature results to be far from thermomechanical critical condition. On the contrary, the baking temperature T = 220 °C presents some critical issues. The achieved results are propaedeutic to make more detailed choice in the following design steps, such as the probe fixing solution, the bolt dimension and the materials. When detailed pick-up coils mounting solution will be defined, the stresses on the contact region between the pick-up coils and the vacuum vessel accurately evaluate.