[Hallb] [New Logentry] Follow-up Re: Follow-up Re: HallB torus burp

kashy at jlab.org kashy at jlab.org
Wed Aug 23 19:00:02 EDT 2023

Logentry Text:
So with the two blowers pumping the vacuum was recovering. at about 15:00 we shut down both the upper and lower turbo pumps to let them coast down to 0 Hz and then at ~16:00 we opened both turbo gate valves in manual and started both turbos.
The lower one successfully made it to full speed and the backing pump which was suplemented by a second backing pump in parallel kept the interstage vacuum to less than 0.2 torr. The upper vacuum pump set only had the original backing pump and the interstage vacuum was holding at about 1.6 torr. Calvin and I then closed the gate valve to the upper turbo and shut down the both the turbo and the backing pumps. We added an additional backing pump just like the one that Denny added to the lower pump set. When we started the upper turbo the backing pressure stayed low (<1 torr) and quickly reached 10-2 torr. We were able to put the lower turbo system gate valve in automatic because the sensors that allow the valve to remain open when the valve controls are in auto were met. We looked through the documentation and found some info that said sensors must be below 1E-4 torr. For the upper turbo some sensors are above and some below. the one listed CG8100T is listed, but that sensor i!
 s not diplayed on the control screen. It might be that the documentation is incorrect and the actual sensor is CG8100TB. That sensor was at ~3.6E-3 torr it was falling but quite slowly and then looking like it was leveling off. At 17:55 I suspected that the blowers were reaching their ultimate pressure and possibly backstreaming into the turbo so we isolated both and shut them down. The pumpdown curve then had an inflection point and slope change. At 18:45 the pressure on CG8100TB is down to 1.55E-4. We will try to switch the gate valve to auto tomorrow morning. 

Finally one more observation. The vacuum in the torus got so bad that the LN2 reservoir could not hold level and the heat shields warmed up to ~150 K on the outlet. Now with both turbos running and the vacuum improving the LN2 reservoir is filling and most of the heat shields are down to less than 90K on their outlet temps. Coil F is at 150K and starting to fall fast.

I'll check again when I get home.


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