Minutes of the LCU Section meeting

Summary notes of the LCU meeting on 13/12/2013

Present: JB, RB, OD, SF, MF, MG, PH, JJ, ASL, YL, VM, SR, THBP, RT, AV

Report from meetings

SLM and general information -> MG
Massimo reported that following the discussion at the past BE workshops, the decision has been taken to define a term to the section leaders. The current term will end with the mandate of the current management, i.e., at the end of 2015. The generic mandate is going to be prepared by HR.
Massimo reminded to send the travel plans for 2014.
Massimo mentioned the current situation of FCC-related studies. The level of resources allocated to these news activities has not been defined by the top management, yet. Therefore, no commitment should be taken. In particular, the FCC kick-off meeting should be considered as an informative meeting, without any commitment in terms of work to be done.
Collimation status -> SR
Stefano announced a new OPAC fellow position at Royal Holloway with maybe up to 30% presence at CERN.
HL-LHC PLC meeting -> RB
Roderik presented the latest ideas/proposals for the parameters to be used for aperture estimates for the HL-LHC studies. A note will be prepared to document the outcome.
The activities for the 11 T dipoles will be streamlined in LCU. All the tools will be made available from the official repositories. A joint meeting between WP2, 5, and 11 will be organised to discuss the future steps.
Space reservation for the stochastic cooling system in IR4 has been discussed: a more centralised system of space reservation should be enforced.

Estimate of beta-beating for 2015 -> ASL (slides)

The past estimates based on the analysis of the magnetic field model at 7 TeV have been reviewed.
The effect of fringe fields on the quadrupole gradient is rather small (1%) in terms of induced beta-beating.
The saturation of the triplets has been neglected: including it makes the beta-beating explode (60% in the worst case scenario).
The b2 in the dipoles and the MQTs are important to have a reliable optics model to be used for the beta-beating corrections. On the other hand, it is decided that fringe fields should not be added in the nominal model, so that the optics is matched including them.
Few points should be checked in more detail:
- Hysteresis effects in the triplets of IR2/8 as they are ramped down at top energy.
- Effect of saturation effect at 6.5 TeV, i.e., whether these are really different from 7 TeV.
- Is the saturation effect in MQXs a random effect changing from magnet to magnet?
Improvements to the segment-by-segment optics reconstruction technique have been presented: simulations of the residual beta-beating after correction with the latest developments and the information on the magnetic field model at top energy will be performed as next step.

Actions from the LHC OMC review -> THBP (slides)

Several items have been reported as a follow up of the OMC review performed earlier this year.
Of particular relevance and usefulness is the on-line measurement and correction of the linear coupling. This will be made possible by the new DOROS system.
The AC dipole will be capable of exciting the beam for more turns. However, due to the higher energy, the beam intensity that can be used for optics measurements will be lower than at 4 TeV. This should be taken into account when reviewing the number of turns needed to achieve a good resolution in the measurement.
The OMC codes have been improved as well as the GUI.
The measured optics will be made available to LSA. Furthermore, the on-line model should be considered as a means to provide a snapshot of the LHC status.

Brainstorming on Post-L1 optics -> SF (slides)

A review of the possible optics configuration for LHC after LS1 is given by Stephane.
Several improvements are presented, either triggered by the need to improve the past optics, but at constant phase advance (e.g., IR6 optics), or to improve the optical configuration, but with a different phase advance (e.g., IR2 optics), or in view of using the ATS as operational optics.
Some of the issues discussed have to do with plain beam physics arguments, some with operational aspects.
It should also be considered that the optical parameters for the high-luminosity insertions will not be pushed since the beginning of the physics run, but a ramp up in performance is to be expected. This consideration should also be taken into account as, rather than defining a single optical configuration, the most flexible one should be selected.
In addition to the optics configurations presented, there are questions on, e.g., the choice of beta* at injection in IR1/5 (to be used in view of reducing the length of the squeeze at top energy) or the choice of the injection tunes. These aspects are independent on the actual optics configuration selected.
The final validation of the new injection crossing scheme for IR8 presented earlier this year at the LMC to cope with 25 ns bunch spacing and generic polarity of the LHCb spectrometer is still pending from injection experts.

AOB

Last update: 6-December-2013

MG & HB

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