I opened the back plate and removed the back insulator. It looked very dirty, and the measured resistance was less than 6M Ohms. Undoubtedly the back bushing is the key to make the x-ray anode trigger failure. It's incredible that the back bushing bacame black dirt after running a month. I think it may be caused by the surface grease when we installed it? By the way, the Viton O-ring 348 to sealthe epoxy block and aluminium plate looked coarse, maybe this caused gas 
leaking? When I removed the x-ray cathode bar, I found one of the binding nuts used two o-rings for sealing, maybe this carelessness caused the leakage?We polished the epoxy bushing using the scouring pad and cleaned it with Kimberly wipers and ethanol. After all the resistance became larger than 50G Ohms.
Otherwise, the resistance between cathode and ground became 1.6M Ohms, it's very low. So we removed the cathode bars to clean them again, make sure the cathode is open to the ground.
2 comments:
I saw the X-ray anode bushings on the blog -- yuk!! Have they ever looked this bad before?? I intend to talk with Chuck Tallman tonight to check whether or not the ground end bushing had grooves at Los Alamos. To first order, it doesn't make since to just have grooves on the input end of the x-ray anode since the electric filed stresses are probably similar on each end. Anyhow -- I will let you know what I find out.
I checked with Chuck Tallman and the ground end bushing at Los Alamos was a smooth cone as is shown on your blog. Originally, Beta delivered each x-ray anode bushing with some metal grading rings but the bushings failed, particularly on the input end. The input end was replaced by the grooved Epon 825 epoxy bushing that you have. The end near ground was replaced by the simple smooth cone and of the same Epon 825 epoxy. I guess I am now convinced that all changes made at Los Alamos did indeed get incorporated on the UIC device.
The pictures of the Epoxy bushings look unbelievably dirty on your blog. It's hard to imagine how they got so bad; especially, in just one month of operation. If I recall correctly, the X-ray anode is at high vacuum via a diffusion pump. Is possible that the oil of the diffusion pump backstreamed into the x-ray anode chamber and condensed onto the bushings??
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