Passive protection of the ITER diagnostic mirrors

Abstract

A conservative engineering model of the impurity deposition on the diagnostic mirrors is proposed. The model is applied to analyze numerically the effect of protecting structures (ducts) with and without baffles in the conditions of the ITER main chamber. It was found that the gross deposition rate in the ducts with baffles, if they are long enough, can be made by an order of magnitude smaller than that in the ducts of an equivalent length without baffles. This model prediction can be tested experimentally. The calculated efficiency of the impurity flux attenuation depends strongly on the model assumption: the variation between the ‘best’ and ‘worst’ cases reaches two orders of magnitude. A case study with the real 3D geometry of one specific diagnostic, core-CXRS, is conducted. For this particular geometry, the effect of baffles is nearly marginal; that is, this is not a universal solution.