Diagnostic first mirrors for burning plasma experiments (invited)

The current state of investigations of the problem of providing first mirro rs (FMs) for diagnostic systems in a reactor-grade fusion device is summari zed. Results obtained in simulation experiments that have been conducted du ring recent years in several laboratories are presented. Attention is conce ntrated on two processes that can have an opposite effect but both can lead to degradation of mirror optical properties, namely: sputtering by charge exchange atoms which leads to erosion, and deposition which leads to surfac e contamination. It is shown in the analysis that when sputtering dominates , mirrors of monocrystalline refractory metals (Mo, W) can have a sufficien tly long lifetime even for FMs that have to be located close to the first w all. Similarly, films of low sputtering yield metals on high thermal conduc tivity substrates (e.g., Rh on Cu) can be used for FMs in locations where t he charge exchange flux is reduced to about a tenth of that at the first wa ll. However, deposition poses a serious threat to the lifetime of FMs but m ore modeling and experimental investigations are necessary before quantitat ive conclusions can be reached. Some mitigation methods are possible and th ese are briefly discussed. (C) 2001 American Institute of Physics.