Experimental Study of First Mirror Degradation Under Influence of Iter Relevant Conditions

Abstract

Being placed in a straight view of burning plasma the First Mirror (FM) is one of most critical elements of ITER diagnostics. The sputtering by charge exchange atoms (CXA) and the deposition of contaminating films and dust on a mirror surface will be the main reasons of FM reflectivity degradation under ITER conditions, and for laser diagnostics the thermomechanical stresses occurring at every laser shot may accelerate the mirror destruction [1]. The materials traditionally used for optical mirrors are not suitable for building-up the ITER diagnostic mirrors. The use of mirror with reflective coating from metals with low sputtering yield and sufficiently high reflectivity (e.g., Rh, Mo, W, Ag) on metallic substrate is one of the possible variant of FM choice for a survival in extreme ITER environments [2]. The production practice of mirrors with Rh and Mo coatings on SS and Mo substrates (Rh/SS and Mo/Mo, correspondingly) by means of sputter deposition of reflective coating on polished substrates is elaborated using a dc planar magnetron [3]. The influence of main damage factors on FM prototypes and experiments on a remote cleaning of mirrors from carbon films by pulsed laser radiation are considered in the paper.