The first mirror(FM)samples made of polycrystal(PC)stainless steel(SS),molyb-denum(Mo)and tungsten(W)were mounted at different locations in HT-7 tokamak to investigatethe surface modifications caused by erosion and deposition.The optical transmission character-istics of first mirror samples were measured by a spectrophotometer.It was found that differentirradiation environment had different influences on the first mirror surfaces,especially with waveantenna nearby.In addition,the erosion made the reflectivity of FM degrade to some extentsas a whole.But the deposition on the mirror influences more than erosion does.Comparing themirrors of SS,W and Mo,irradiated in the same environment,the W-mirror had the least changesin reflectivity with regularity,while the SS-mirror had most serious changes.
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