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Expert discussion on scenarios for operating with sparking RF Fingers
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Videoconference
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
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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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