Change of the optical reflectivity of mirror surface exposed to JET plasmas
There is only little knowledge about the change of the optical reflectivity of different materials due to charge-exchange (CX) bombardment. In order to get more insight into the mechanisms resulting in changes of the reflectivity, the surface modifications and the reflectivity change of carbon, aluminium and nickel samples exposed to Joint European Torus (JET) plasmas have been examined. From these results lifetime predictions for mirrors used in the international thermonuclear experimental reactor (ITER) can be obtained. The optical reflectivity of erosion dominated carbon and aluminium surfaces from the inner torus wall decreases by a factor of between 2 and 3 after exposure to about 2000 JET plasma discharges. The erosion is due to sputtering by charge-exchange hydrogen and He glow discharge cleaning. The decrease of the surface reflectivity is mainly due to surface roughening of eroded surfaces and change of the chemical composition of the surface. The roughness of eroded surfaces increases with increasing total erosion. The change of the chemical composition of the surface layers at the JET conditions is material dependent. Samples located at deposition dominated areas show thick deposits. The reflectivity of these samples decreases to nearly zero.
Bibliographic Reference: Article: Diagnostics for Experimental Thermonuclear Fusion Reactors 2 (1998) pp. 279-286
Record Number: 199811106 / Last updated on: 1998-09-28
Original language: en
Available languages: en