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FCC-FS EPOL group and FCCIS WP2.5 meeting 24
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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.
List of actions:
Experiments:
- Could a Compton polarimeter be installed at KARA? At which cost and which design is needed?
- What is the available space for polarimeter at KARA and could a beam line be used?
Polarization:
- Vertical dispersion matching to be followed up.
- What is the impact of orbit bumps on vertical dispersion and emittance?
- How does it look for W?
- What is the impact of BPM errors?
Effects on ECM:
- A broad study is required to understand the cross-talk between IPs with different collision offsets and OSVDs.
- What is an acceptable value for a RF-frequency shift (dp/p ~ 1e-4?) for OSVD for colliding bunches?
- Define parameters (strength, rise time, etc.) and suitable locations for kickers measuring OSVD for pilot bunches.
Polarimeter:
- Can we benefit from more than one polarimeter, and if yes, at which cost?
- What are the systematics for RDP and FSP measurements?
- What is the best location for one polarimeter?
- How stable is the laser wavelength's central value, laser polarization and spectral width and what is required for RDP and FSP measurements?
- Which laser systems are applicable for pilot bunches and which for colliding bunches?
- How many scattering events do we need for which photon detection efficiency and polarimeter detector requirements?
Depolarizer:
- What are the systematics for RDP and FSP measurements?
- Which minimum beam polarization level is needed (is less than 10% ok) ?
- What is the presently foreseen operation mode (collision on and off or continuously on)?
- Where is the best location for a depolarizer (would next to the final focus work)?
- If the kicks are not closed, what would be the impact on the optics?
- Could the system be combined with the feedback system?
Monochromatization:
- What is the impact of beamstrahlung on monochromatization?
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