U. Breuer

First studies of ITER-diagnostic mirrors in a tokamak with an all-metal interior: results of the first mirror test in ASDEX Upgrade

In ITER, mirrors will be used as plasma-viewing elements in all optical and laser diagnostics. In the harsh environment, mirror performance will degrade hampering the operation of associated diagnostics. The most adverse effect on mirror performance is caused by the deposition of impurities. It is expected that the most challenging situation will occur in the divertor. With the envisaged changes to all-metal plasma-facing components (PFCs) in ITER, an assessment of mirror performance in an existing divertor tokamak with all-metal PFCs is urgently needed. Molybdenum and copper mirrors were exposed for nearly nine months in ASDEX Upgrade which has all-tungsten PFCs. Mirrors were located at the inner wall, under the dome and in the pump duct. During exposure, the mirrors were heated to temperature in the range 145?165??C. This was made to approach the expected level of heating due to absorption of neutrons and gammas on mirrors in the ITER divertor. After exposure, degradation of the reflectivity was detected on all mirrors. The highest reflectivity drop was measured on mirrors under the dome facing the outer strike point, reaching ?55% at 500?nm. The least degradation was detected on mirrors in the pump duct, where the reflectivity was preserved in the range 500?2500?nm and the largest decrease was about ?8% at 250?nm. On all contaminated mirrors carbon fraction did not exceed 50 at% while the major contaminants were metals and oxygen. The degradation of exposed mirrors underlines the necessity for urgent R&D on deposition mitigation and in situ mirror cleaning in ITER.

Castellated structures for ITER: the influence of the shape of castellation on the impurity deposition and fuel accumulation in gaps

Castellated structures are proposed for the first wall and divertor area in ITER. However, there is a concern that impurities and fuel will be deposited in the gaps of castellation leading to the undesirable tritium inventory. Optimization of the shape of cells in the castellated structures appears to be a possibility to reduce the impurity transport and fuel accumulation.A new tungsten castellated limiter has been exposed in TEXTOR. The castellation cells of the rectangular and of the roof-like geometries were exposed under the same plasma conditions, allowing a direct comparison of the carbon transport and fuel inventory in the gaps. The gaps of shaped cells contained a factor of 2–3 less carbon and deuterium, in comparison to those of rectangular cells.