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Expert discussion on scenarios for operating with sparking RF Fingers
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874/R-018 - salle de réunion activité CCC (CERN)
Machine Protection Panel
Zoom Meeting ID
94542110238
Description
Zoom room for the Machine Protection Panel
Host
Daniel Wollmann
Alternative host
Christoph Wiesner
Useful links
Join via phone
Zoom URL
07.03.2024
Expert discussion on scenarios for operating with sparking RF Fingers
Indico page: https://indico.cern.ch/event/1390492/
Participants:
Giuseppe Bregliozzi, Andy Butterworth, A. Lechner, Belen Salvachua, Josef Sestak, Matteo Solfaroli, Helga Timko, Jan Uythoven, Christine Voellinger, C. Wiesner, D. Wollmann, Carlo Zanini,
Introduction. Follow-up topic of discussions at the Chamonix workshop.
How to be prepared in case we get issues with the RF fingers and prepare a procedure to be applied in this case.
Main points to cover:
- Can we run with sparking RF fingers and under which conditions?
- What interlocks need to be adapted? Under which conditions could we allow to operate and delay a repair to the YETS?
Warm-Module RF Fingers - recap of issues observed in 2023 and repairs in EYETS 2023/24 (Giuseppe)
- Overview of layout in section A4L1 (symmetrically R1, L5, R5):
- 9 modules after TAN and 6 elliptical modules before the triplet; there is only one vacuum gauge (not interlocked) and no sector valve; next sector valve is at the triplet (also with interlocked gauge).
- Consolidation during YETS 2023/24:
- All modules in the affected sector were changes, with DRF modules interleaved with anchored modules ;
- Elliptical modules have not been consolidated, just springs repaired, where required. … two springs oo 24 were found damaged.
- One DRF at each side has been installed around the BSRT (pt4)
- Point 8: after TDIS one module was changed, which showed issues, 5 other modules where not changed
- Point 2/8: was not touched around TDIS and TCDD can be done very quickly, as it has very short sectorisation.
- Point 2: large vacuum chamber after the ZDC is critical, due to a large volume and long takeout in case of an intervention. The proposal is to install bellows without RF fingers, as there is no design for this diameter;
- Point 4 as well untouched;
- No elliptical modules were changed;
Discussion:
- Is there any concern to run with these type of conditions. In pt2 we have been running for a couple of years in this condition; worst case would be to damage the bellow if the RF fingers touch the bellow.
- For the moment no detectable precursors have been identified, which indicate that the spring gets damaged.
- Pressure interlocks close to cold machine parts should not be increase beyond 10-6mbar, to avoid pollution of the beam screen surface, which could lead to increased heat load.
- RF fingers could move in the aperture, this would be detectable due to the beam losses.
- No significant increase of activation expected due to increased vacuum pressure at a damage module
Follow-up:
- Review if there could be a collateral damage on accelerator equipment which makes the situation worse and request for an immediate intervention - Giuseppe
Recap of BLM threshold changes in 2023 due to failure in VMBG in LSS1 & related studies - Anton
- Beams dumped always by one BLM (BLMQI.03L1,B2E30_MQXA)
- BLM thresholds were increased at Q3 after the intervention (MF0.16 —> 0.25)
- Impact of beam gas collisions depends closely on the position, makes strong difference
- Based on experience from 2017 (septum event), the pressure will likely reach a (lower) steady state following the highest levels at moment of failure and shortly there after.
Follow-up:
- Estimate energy deposition in the triplet before the repair the warm module with full beam & estimate the expected energy deposition in the triplet, if the closest module before the triplet would fail - could quenching of the triplet be avoided? - Anton
- Look back at 2017 LHC septum issue and summarize and derive observed time scales before situated settled in a stable regime. Compare vacuum levels during peak of event and during stable period - Josef
First level action steps:
- If issue with RF fingers is detected, stop operation and take X-rays to identify the source module
- Perform FLUKA studies to estimate the expected energy deposition in the downstream coils to identify possible safe intensity levels for operation, without risk of quenching.
- Some low intensity operation to cover the time for FLUKA studies
Follow-up:
- Prepare first version of procedure in shared document - Daniel
Next meeting: Thur 14.03. 10:00-11:00
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