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FCC-FS EPOL group and FCCIS WP2.5 meeting 30
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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.
Videoconference
FCC-FS EPOL group meeting
- Zoom Meeting ID
- 63437787216
- Host
- Alain Blondel
- Alternative host
- Jacqueline Keintzel
- Useful links
- Join via phone
- Zoom URL
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R. Kieffer presents updates on the FCC polarimeter. The baseline is to install them in IP1, which requires an extension of the bypass tunnel. The distance between the beams is about 6 m. A BDSIM model has been designed from the LIP to the exit window chamber. For example at Z, the width of the compton electron pattern is about 300 mm at the exit window and 1160 mm 96m after the extraction. At ttbar, this is increased to about 4 m. It is therefore suggested to reduce the distance between the Si-detector and the beam to keep a transverse width of 300mm, leading to moving the detector closer to the LIP. The angle of the extraction window is currently 15°, defined by, among others, impedance, thickness of the exit window, crossing of the pixel detector etc. G. Wilkinson comments that it should be checked that this would also be ok for calibration runs during ttbar-run. Ideally the detector is aligned with the same angle as the exit window, about 1 mm away. T. Lefevre suggests to study intermediate solution of fully transverse vs 15°. T. Lefevre asks is all these distributions should be measured, where A. Martens confirms. Furthermore, 1 mm aluminium is the most transparent solution. Following a question by T. Lefevre, R. Kieffer answers that backgrounds would be included in BDSIM. G. Wilkinson comments that 1 mm could possibly be reduced. It is suggested to answer the question what would be the benefit of having one polarimeter per IP and beam. T. Lefevre comments that as a compromise one could think of having 1 bypass tunnel in PA (permanently available) and the others in the alcoves (not permanently available). Following a question by W. Höfle, it is confirmed that the location of the polarimeter and the depolarizer do not need to be in the same location. Following a question by J. Keintzel, A. Martens comments that in case longitudinal polarization for pyhsics bunches could be achieved, by injecting polarized bunches, this system would work, but then one polarimeter per beam per IP would be required.
W. Höfle has started working on the depolarizer. It should be investigated if mainly the magnetic field will be used. It is aimed that this device could be combined with the transverse feedback system.
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