[Tgun] [Revised Logentry] 9/17 GTS Update

[mstefani at jlab.org]

Logentry Text:
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After yesterdays PSS trip with arc at 140kV, the turbo and HVPS do not function properly.  There is high likelihood that other components of the beam-line have been damaged. A full assessment needs to be done, but a quick check indicates issues with camera/viewer controls along with the known damage to picoampmeter, flow-meter and now the turbo & power supply.

We opened the gun today and found many metal shavings in the ceramic close to the HV end. The shavings were on that same side of the stalk with the most FE sites and shavings could be seen "welded" to the stalk at FE sites. This was on the bottom of the ceramic/stalk and the highest radiation readings were from the bottom of the gun. The shavings were likely trapped behind the triple-point shielding in the ceramic. A significant amount of evidence suggests this is the cause of our issues with non-successful HV processing. 

The fact that the PSS tripping is not dependent on which PS we use, indicates that a Faraday cage is absolutely necessary for operation.

The cathode was removed and checked in the source lab nitrogen box; no visible damage can be seen. When we do resume HV processing, I think it would be safe to install the cathode rather than a blank flange and have to reopen to install the cathode.

Suggested Action:
Damage/Cost assessment
Polish electrode/stalk
Clean ceramic (completed)
Build/Install Faraday cage
Group meeting on moving forward


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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3731870
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