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FCC EPOL group meeting 54
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Europe/Zurich
354/1-019 (CERN)
Description
The FCC technical and financial feasibility study comprises a work package (EPOL) on precision determination of the centre of mass energy at FCCee. using resonant depolarisation of the beams, in conjunction with precise measurement of the energy spread and other parameters using physics events in the detectors, and other beam diagnostics in particular to control the collision parameters. Specific equipment involves polarimeters for both beams, polarisation wigglers, and depolarising RF kickers. The possible mono-chromatization of the beams in view of a measurement of the e+ e- —> H (125) process will also be studied and special requirements investigated.
Short group meetings are foreseen at 15:00 on Friday.
FCC-FS EPOL group meeting
Zoom Meeting ID
63437787216
Host
Alain Blondel
Alternative host
Jacqueline Keintzel
Useful links
Join via phone
Zoom URL
Follow Ups:
- Status of ELSA:
- In-situ detector calibration, integration for di-muon events --> News in one of the next meetings
- Tuned lattice repository -> Ongoing work within the tuning working group
- Polarimeter dipole discussion --> Discussion took place 28 August, summary and actions below; next meeting foreseen end of September/beginning of October
- EPOL talk at ICHEP --> Juba presented
J. Keintzel reports about discussions for the polarimeter dipole.
Meeting 28 August to discuss about the polarimeter dipole:
Short summary:
- Uniformity of ~2 units through full magnet (not only integrated)
- Stability ~ 10 ppm over 30s to 1min
- Field measurements challenging
- Roll error of 150 um to 200 um already achievable today, 100 um challenging
- 17 m long dipole challenging in many aspects (transport, field measurements, alignment etc.), if split in 2 fringe fields to be evaluated
- 120 mm horizontal stable field region, single aperture
Actions:
- Jacqueline: check with Marc-Andre 17 m long dipole (other requirements, splitting in new optics version?, etc.)
- Melvin: check with magnet colleagues and provide field map
- Robert, Aurelien: evaluate polarimeter performance using realistic field map, including dipole stability and roll error
Regarding the dipole, E. Torrence comments that 14 m length would be acceptable since this is the length of dipoles for the FCC-hh. R. Kieffer adds that SR etc should then be checked.
J. Keintzel reports that A. Blondel has suggested to look into longitudinal boost measurements with cosmic boosts.
R. Kieffer presents updates on the polarimeter. Since the Compton end point does not scale as much, the sensor should be placed closer to the LIP. He presents the layout of the polarimeter chambers for the Z mode. It has not yet been discussed with other teams (vacuum, mechanical engineering, etc.). It is proposed to have 1 polarimeter per beam optimized for Z and another one for W for 3D polarimetry, requiring the electrons too. RDP will still be possible, but monitoring longitudinal polarization challenging. C. Carli asks about if a compromise would be possible.
E. Torrence comments that the most important part is the outer most part.
H. Bartosik asks about the winglets and the impedance. R. Kieffer answers this is proposed for impedance considerations.
R. Kieffer presents thoughts on the polarimeter for the booster.
Currently the laser alcove is removed, to be followed up with integration team and TIWG.
Regarding RDP at ZH, backgrounds should be checked.
Follow up:
- Integration of laser alcoves
- Polarimeters up to ZH to perform RDP and best compromise
- Polarimeters in booster and injectors
- Error estimate at each energy mode assuming different set ups
- Fitting activities
M. Watson presents on the polarization ring. Polarization after errors and corrections is above 92 % for all studied seeds. Polarization time is about 12min.
Follow up:
- Longitudinal polarization to be studied for special Higgs Run
- Optimized design
- Operational scenario (regularity of RDP, lifetime, etc.)
J. Wenninger presents an update of polarization and RDP for LCC 107 up to ZH energy. Currenlty up to 70% transition in the booster could be transported. It is reminded that with 10% polarization over 22s one gets 1% error (at every scan point). RDP could, potentially be performed up to ZH energy.
D. Barber comments on spin flipping in presence of radiation
Follow up:
- Overlap RDP scans with detector resolution
- Check lifetime and polarization lifetime of bunches
- Single exciter vs 1 arc vs bump: impact on SR, impact on spin tune, background
J. Wenninger presents on local IP energy offsets due to energy sawtooth. b1 error in dipoles give a rms below 1 keV. Tuned seeds gives 2 to 7 keV rms. The average energy is shifted by -0.2 to -0.4 MeV. A. Blondel adds that boosts also help to determine the difference between pilots and colliding bunches.
Follow up:
- Add impendance losses
- Difference between pilot and colliding bunches
- Calibration with cosmic muons and shaft locations
A. Blondel presents considerations between longitudinal polarization vs monochromatization. He reports that S. Gilardoni highlighted that the injectors should be designed in a way to allow for adding the possibility to collide longitudinal bunches later.
J. Wenninger comments that CEPC colleagues use a spin rotator.
Follow up:
- Evaluate monochromatization vs longitudinal polarization for 125 GeV Ecm (physics, max pol and lumi from accelerator)
- Possible organise 1 day workshop
M. Switka presents on the ELSA Compton polarimeter (Bonn University). Measurements at high and low energies agree well with BDSim, while some differences or the mid-energy - tbd.
R. Kieffer adds that in parallel one could find other ways to collaborate with CERN.
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