The place to discuss the LHC. Commissioning, operation, issues, events ....
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Tau
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by Tau » Wed Nov 24, 2021 8:19 am
dukwon wrote: ↑Tue Nov 09, 2021 1:07 pm
The "ULO" has been identified as a buckled RF finger, so sector 23 will be warmed up for an intervention. This delays the restart by several weeks. (However, better to catch it now than then!)
I see S23 is at room temperature now; I guess they're already fixing it as we speak.
And then the way for cooling down can begin again
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trobbins
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by trobbins » Sat Dec 04, 2021 10:18 pm
Still at room temp.
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dukwon
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by dukwon » Wed Dec 29, 2021 10:27 pm
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Tau
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by Tau » Tue Jan 18, 2022 8:03 am
That's a pretty good read. What I learnt from there are a few things I didn't know yet:
- Even CERN engineers are fallible , as proven by a magnet with swapped polarity
- The ULO didn't stop them from actually do a full ramp with stable beams, albeit with low intensity
- This enabled the experiments to do some very needed testing!
- I also found it interesting to see that even a very minor shielding issue (a shielded cable that was too close to a shielded beam tube) already can decrease beam quality.
The placement of devices and cables is more important than I realized.
And in the mean time, the temperatures are dropping again. Can't wait until we have full green on the cryogenics vistar. Up to a good 2022!
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Tau
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by Tau » Tue Feb 01, 2022 7:50 am
Thanks for the
dash.web.cern.ch resource. I've been clicking away looking at the pretty pictures!
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trobbins
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by trobbins » Tue Feb 01, 2022 11:52 am
They seem to be in the 'final straight' so to speak, with getting all the parts down to operating temp. The plots obviously miss a lot of detail of what sub-assemblies/lines are getting flow through them and why, as indicated by some changes in refrigerant flow/pressure.
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dukwon
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by dukwon » Tue Feb 01, 2022 1:21 pm
Here is the aforementioned buckled RF finger found in 21L3
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Attachments
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- buckled_finger_tomography.jpg (26.77 KiB) Viewed 13050 times
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- buckled_finger.jpg (54.33 KiB) Viewed 13050 times
Last edited by
dukwon on Tue Feb 01, 2022 1:54 pm, edited 3 times in total.
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dukwon
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by dukwon » Tue Feb 01, 2022 1:23 pm
Since we're (slowly) discussing YETS, I've added it to the topic. I suggest making a new thread "2022 operations" in March
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Tau
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by Tau » Tue Feb 01, 2022 3:08 pm
dukwon wrote: ↑Tue Feb 01, 2022 1:21 pm
Here is the aforementioned buckled RF finger found in 21L3
Wow. It is cool, and a bit sad, to actually see what caused the delay of several months. But anyway, we're almost there.
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dukwon
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by dukwon » Tue Feb 01, 2022 7:48 pm
Here's a description of RF fingers
from the ESRF website
To absorb chamber-to-chamber misalignment and thermal expansion, [...], bellows are used to inter-connect a large number of chambers along the ring circumference. These bellows, however, are seen as resonant cavities by the beam hence breaking the geometrical continuity of the beam pipe and leading to degraded vacuum and stability.
The continuity is restored by electrically shielding the bellows from the beam using so-called RF fingers which consist of conductors matching the vacuum chamber profile and connecting the beam pipes on either side of the bellows. The RF fingers are meant to absorb mechanical movements while providing the best possible electrical and geometrical continuity
Here's a cutaway model of a bellow, where several RF fingers are visible:
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dukwon
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by dukwon » Tue Feb 01, 2022 7:49 pm
Here's my cartoon guess of what happened:
Essentially, the finger must have buckled somewhat at low temperature, then at the warm-up in Feb 2019, it was bent even further by the gap closing due to thermal expansion.
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trobbins
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by trobbins » Thu Feb 10, 2022 4:56 am
Nearly all alarm states are back to green on the LHC Cryo dashboard for S23. They appear to have been exercising a lot of cryo facilities over the last few days, with alarm states changing a few times.
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dukwon
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by dukwon » Wed Feb 23, 2022 12:21 pm
All sectors cold, powering tests ongoing. After cavern closure (24th March) Sector 23 needs a new magnet training campaign: ~20 quenches, 2 weeks estimated, then ready for beam injection.