Arcing from LLG-TWIN excimer inside

When I ran the TWIN excimer amplifier, I could hear the crack sound inside the chamber. This phenomenon was happened before, which was caused by the spark from the Thyratron plate and ground plate. I put two picece of plastic sheet to isolate them. Probably the sheet became dirty or they were too thin. The Thyratron plate should be tightened with the real ground plate in order to avoid the spark, however it will take several days to remove the plate to drill the holes for tightening. The simple way is to replace the isolating plate with a new teflon plate. After replacing, the system ran well.