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FCC-FS EPOL group and FCCIS WP2.5 meeting 32
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Europe/Zurich
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 16:30 on Thursday typically every three weeks.
FCC-FS EPOL group meeting
Zoom Meeting ID
63437787216
Host
Alain Blondel
Alternative host
Jacqueline Keintzel
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J. Keintzel reminds that K. Oide presented a new non-local solenoid compensation scheme in the MDI meeting last Monday. This scheme produces 1 per mille longitudinal polarization, at least at the IP. In addition J. Wenninger pointed out that this also applies a spin rotation which could limit the achievable polarization. Y. Wu will study this new scheme with BMAD.
C. Kiel presents her final results of her 8 weeks internship of a toy model to simulate RDP. It is found that the step size of the depolarizer process influences measurement results, and the polarization after the scan.
D. Barber comments that with SR that the spin will not be flipped completely due to decoherence. C. Carli suggests to also include betatron oscillations. D. Barber comments that an AC-dipole and the generated betatron oscillations will impact the resonance strength and should be carefully studied. J. Wenninger comments that the idea is to have 2 depolarizers with 180deg seperated. I. Koop comments that it would be best to investigate in a more realistic model.
R. Kieffer presents simulations on the SR background of the last six dipoles with BDSIM after the extraction window, to evaluate the SR background on the detector for the Z-mode. Using MC simulations, with 10 mm of copper thickness, about 4e11 will pollute the detector for phyiscs bunches. On average 2 SR photons per electrons are emitted. 1 compton electron for 100 SR photons are expected, which imposes challenges for the polarimeter design. BDSIM shows a different energy distribution which is currently being investigated. All designed polarimeter chamber designs do not show a significant contribution to the total impedance, as simulated by M. Miglorati et al. G. Wilkinson comments that the SR photons will have a different energy and so he thinks this can make it easier to distinguish them from the electrons. G. Wilkinson comments that copper will lead to a lot of scattering which will disturb the pattern. Following a question by J. Wenninger, R. Kieffer comments that the biggest contributor of photons is the last dipole. Also, there could be shielding for the SR from the other bends.
R. Kieffer presents the status of the CE for EPOL. The laser hutch could potentially be installed in the first big alcove, which would then be moved about 130m away from the IP. For redundancy one could install 2 polarimeters per beam, possibly each with 2 lasers. This means, that the laser room is not accessible during operation. J. Wenninger comments that during the start of operations the lasers were tuned all the time. R. Kieffer comments that E. Ganis wants to investigate how this can be tuned fully remotely. G. Wilkinson comments that if there is no access more than one polarimeter is mandatory.
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