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Session 4 preparatory meeting for LIU Workshop
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Europe/Zurich
6/2-008 (CERN)
- Extend session by twice 5 minutes (for Alex and Hannes' talks) ⇒ Action: Giovanni and Heiko to seek and implement the extension
- Nominal 25 ns beam
- 2021: Recovery of pre-LS2 beams (reasonably LHC multi-bunch beams, nominal for scrubbing, BCMS for operation, ready by mid-summer - as currently the start of the LHC is foreseen in May 2021)
- End of 2022: First step of intensity ramp-up up to 1.8e11 p/b, reach design brightness. However, in the subsequent discussion, it appeared that the ramp up of the brightness could not be straightforward in the PSB and PS, so perhaps a smoother achievement of the design brightness could be envisaged (also it seems that the intensity would be first of all required)
- 2023/2024: Then intensity ramp up at constant design brightness
- End 2023: Target 2.1E11 p/b
- End 2024: Target 2.3E11 p/b
- BCMS beam
- End 2022: Recommendation from LHC Run 3 Configuration WG in Evian 2018 → 1.8E11 p/b in 1.3 um (perhaps not OK for LHC due to limitations of the beam dump)
- LHC (Rogelio):
- Limitations on LHC dump: only when dumping at top energy and full rings, otherwise higher bunch intensities can be studied with reduced numbers of trains
- Intensity ramp up more important and more critical for LHC than brightness ramp up
- Key points to be checked in LHC: e-cloud and RF, both not sensitive to transverse emittance. Exploring transverse stability would be also an asset. However, studies of halo population for high intensity beams could be also interesting and it would require the nominal LIU emittance
- Intensity for scrubbing in LHC (slightly higher in LHC): Does the LHC need to be scrubbed for higher intensities?
- Doublet beam off the table because no clear interest is seen from the e-cloud point of view and the set up is time consuming
- 80 bunch schemes, still some interest?
- 8b4e with BCMS schemes would be optimum in terms of lumi production if mixed in SPS
- LHC would be interested to see HL-LHC beam at injection flat-bottom in LHC in MDs as early as possible, but also the consequences of learning from these MDs should be clarified (e.g. learning about some high intensity limitations by 2022 or 23 would still leave room to devise and implement mitigations by LS3)
- Rogelio to propose detailed list and agenda
- Wished profile of intensity versus time: the intensity ramp up curve over Run 3 could be tentatively drawn
- PSB/PS (Alexander)
- Extend presentation by 5 minutes
- Separate timelines for brightness and intensity: illustrate needs and all milestones (things that have to be demonstrated) for the brightness ramp up in the PS.
- Exception management: not commit to reaching brightness curve by 2022
- Ions in PS: limitations (microwave instability) and impact of results on protons (multi-batch) - but this could also be included in Theo's talk to make continuity on the ions.
- SPS (Elena)
- PS-SPS transfer: few new results, need to progress with simulations for injection of multiple batches, which is planned to happen with Ivan in 2021
- Impact of 915 MHz HOM, which is only seen with 4 batches due to large Q
- Emittance blow-up will be required, already operational issue as it was not used in the last years due to Q20 and it cannot just turned on as it requires careful setting up: algorithm for emittance blow-up to correctly take into account double-RF and intensity effects
- Bunch-by-bunch variation from PS is important for the correct working of the longitudinal emittance blow up: Alexandre’s studies
- Horizontal instability
- Margin with octupoles and chromaticity will be evaluated for the LIU intensities, now that the behaviour for 1.8e11 p/b has been correctly reproduced in simulations (input from Carlo)
- Electron-cloud and scrubbing (input from e-cloud team through Hannes):
- Need for scrubbing for different steps of intensity ramp up
- Issues with scrubbing while ramping up the intensity
- SPS ions (Theodoros)
- Transverse instability: nobody working at this issue in ABP yet, not a straightforward problem, as it requires even the establishment of a new horizontal impedance of the machine wrt to the dispersive orbit during slip stacking.
- Reference to past experience of instability with radially displaced bunches (seen on signals in all planes and mainly unidirectional, i.e. either when moving the beam inwards or outwards)
- 10 mm radial offset, 0.5 GeV
- 800 MHz system should become operational for ions
- Less noise with the LLRF system is expected to reduce bunch-by-bunch blow-up in SPS at flat bottom
- Action Heiko: Locking of 800 MHz on 200 MHz, just after transition? Should/can this be earlier?
- Draw a tentative MD plan with milestones to be reached for the full commissioning of slip stacking: what can be tested before September 2021, different steps (single bunches, shorter trains, lower bunch intensities to disentangle from intensity effects)
- Upgrade beyond baseline to reach LIU parameters (Hannes)
- Extend presentation by 5 minutes
- Address the question of available MD time for the LIU ramp up and when the possible showstoppers should be identified to put in place corrective actions.
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