Interpretation of Tore Supra in-vessel mirror experiments

Abstract

In this paper the results of post-mortem analysis of mirror samples (molybdenum, stainless steel and copper) exposed for the 1 year experimental campaign inside the Tore Supra tokamak are presented. The mirrors were not protected during the experiment and therefore were exposed both to glow discharge conditioning of the vessel walls and to working discharges. After exposure, all samples were found to be eroded and at the same time were coated with a thin contaminating deposit. We pay attention to the fact, that the observed erosion cannot be described using the published sputtering yields. In particular, the difference between the erosion of stainless steel and copper exceeded a factor of 10 and the difference between the erosion of stainless steel and molybdenum was less than a factor of 2 in comparison with the corresponding factors of approximately 2.5 and apprximately 10 known from the literature. An attempt is made to correlate these observations with the different sticking coefficients of carbon on to different substrates.

Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions

“…Experiments on exposure of Cu, Mo and SS mirror samples in the Tore Supra (TS) tokamak [52,53] have resulted in the discovery of a new effect of mirror interaction with a carbon-containing plasma. The mirrors were arranged close to each other and were open to the plasma during the whole time of their presence in the tokamak chamber, except for a narrow edge around the periphery of the samples, which was closed by the sample holder.…”

“…It was assumed in [53] that in the presence of a graphite limiter in TS, the main reason for the low sputtering of the SS mirror was a high probability of carbide formation on the mirror surface exposed to a plasma comprising carbon ion admixtures, because all main components of stainless steel (Fe, Cr, Ni) are capable of forming stable carbides. During exposure to the carbon ion-admixed plasma, a thin carbon film, having a lower sputtering coefficient (e.g., see ref [55]), is continuously formed, strongly reducing the sputtering of the metal mirror.…”

“…The characteristics of these films are described in refs [65,66], and [53], respectively. The effect of long term sputtering by plasma ions on the appearance of diffusive components was studied for mirrors of different materials by the use of the DSM-2 stand (in IPP NSC KIPT).…”

Modification of optical characteristics of metallic amorphous mirrors under ion bombardment

“…Sputtering dominates only for mirrors that are not covered with any diaphragm, i.e. are exposed to charge-exchange atoms during working discharges and to ions produced by glow discharges used for conditioning of vacuum vessels (JET [21], Tore Supra [22], HL-2A [23] and LHD [24,25]). If mirrors are somehow protected from the plasma impact, e.g.…”

Role of Recrystallization of Tungsten in Formation of a Roughness of Its Surface Under Influence of Successive Action of Neutrons and Sputtering

“…В этом случае комплексный показатель преломления N  n  ik эффективной среды может быть найден из соотношения [14,15]:…”