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SPS BWS Task Force
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865/1-D17 (CERN)
Videoconference
SPS BWS Task Force
- Zoom Meeting ID
- 63016739397
- Host
- Raymond Veness
- Useful links
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Slides are available on the INDICO site here:
Present: Ivan Karpov, Benoit Salvant, Thibaut Lefevre, William Andreazza, Kevin Li, Michael Sullivan, Jonathan Emery, Jose Somoza, Nabil El-Kassem, Ray Veness, , Haiko, Federico Carra, Francesco Velotti (Zoom)
Excused: Christine Vollinger, Federico Roncarolo, Carlo Zannini
Operational beams (Nabil)
Nabil shows a slide on SPS cycle during BWS failure.
Benoit: The bunch length through the cycle was not logged, only at injection. This is why the bunch length on the images does not decrease during the ramp.
2022 beam operations had cycles with a higher intensity, but 2023 beams have a longer flat-top. Kevin: Ratio between intensity and bunch length is key to WS failure.
Discussion on how we should be logging the bunch length. Discussion on how to use the WCM for this purpose. This needs to be fixed/understood for the next TS.
Agreed it would be important to repeat the same operating scenario which caused the BWS failure and measure bunch length. ACTION: Ivan will look at how bunch length measurement can be made and see how to repeat this measurement in the SPS. Tom Levens can help.
Update on Simulation and RF Measurements (Michael)
Original simulations from 2017, updated with Macor and C-wire.
Electrical feedthrough is present in the installed instruments, but no coupler installed and the feedthrough is not grounded.
Further simulations shown in the slides have the feedthrough and coupler installed, so there is some difference from the 'installed' instrument.
Options shown for immediate improvements:
fill-in the gap between shaft and wall, preferably with an RF contact,
change the parking position of the wire/fork assembly.
Noted in the discussion that if we fill this gap, then we cannot use this feedthrough to measure HOM or to extract power.
Summary given with possible mitigations. Explanations given and 'non-RF expert' guide.
Lower Z is good.
Lower Q gives broader peak, which perhaps gives a greater change of crossing a beam harmonic, but with less heat transfer
frequency should not be on a beam spectrum frequency or harmonic,
'Dispersion. on wire' gives the location of the field peaks.
Other options for improvement were discussed: Ferrites, damping resistors, shorter forks. Michael and the RF team will continue to simulate these other options. Commented that If we want to consider adding ferrites, this should be analysed urgently as the lead-time is long. Ask MME (Federico) to start analysing this as soon as possible.
First results on instrument inspection (William)
Some microscopy made in the BI lab, then the fork assemblies were given to MME metallurgy for inspection. First micrographs were shown.
Signs of damage to kapton insulation and perhaps solder melting/darkening. ACTION William: Check which temperatures are required to show these signs of damage.
Carbon filament traces seen on all of the wire ends. No sign that the carbon has 'slipped out' of the copper coating, which was one of the initial theories.
Most carbon ends show signs of brittle fracture. However, some sign of necking on one of the carbon filaments. This is unexpected as carbon fibres should be brittle upto v.high temperature. ACTION William: Follow this up with MME metallurgy.
Discussion on possible actions for TS1
ACTION Kevin: Discuss with the OP community if there are short-term operational mitigations that could be used to extend the possible wire lifetime in case we decide to replace some or all of the scanners during TS1.
Due to the upcoming holidays, it was agreed to hold the next meeting on Wednesday 17th May at 9h00
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