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6th FCC-ee Optics Design meeting
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Europe/Zurich
6-R-012 (CERN)
6-R-012
CERN
Participants: Sandra Aumon, Anton Bogomyagkov, Andreas Doblhammer, Bernhard Holzer, John Jowett, Katsunobu Oide, Pavel Piminov, Dmitry Shatilov, Serguey Sinyatkin, Frank Zimmermann.
Nonlinear Dynamics Study for the FCC-ee collider, by Pavel Piminov.
Pavel performed DA studies in IRs of FCC-ee, by considering a linear lattice outside the IR and for different vertical beta star (0.1,0.2 and 0.3cm). Without the Arc's sextupole, crab, RF nor damping, the horizontal DA is 100 sigma. Adding the arcs sextupoles, the DA goes down to 10 sigma. The energy acceptance is -2% up to around 2.5%.
Pavel performed as well simulations with damping one ¼ of ring (IR to IR): he added 3 points of damping by including in his computation a exponential term. At 45GeV, the DA with damping, RF is about 100 sigmas in horizontal plane and DE is about +/-2%. At 175GeV, DA goes down to 40 sigma in the horizontal plane. In general, Pavel showed that DE and the DA without crab waist is good.
With CW and at 175GeV, the DA drops to 19 sigmas in the horizontal plane. DA limitation comes from the interaction between IR sextupoles and quadrupole fringe fields with the arcs sextupoles. The damping changes significantly the DA and the energy acceptance.
John Jowett make the remark that introducing a exponential factor will ipso facto increase the DA. He reminded that in LEP, the limitation came from the synchrotron radiation in the quadrupoles and it is important to have a good modelization of the radiation damping in the code. The computation done by Pavel were done with a home-made code.
Anton asked to John, from his experience in LEP, for any recipe to optimize the DA. John replied that in LEP, they increased the RF voltage, changed the arc phase advance to 180/60 degrees.
Update about the FCC-ee and pp layout, by Katsunobu Oide.
The difference between the two layouts around the IR went down to approximately 300m. A suggestion from Daniel Schulte to change to make the e-e+ IPs at 90/270 degrees improved the situation. Additional halls for the FCC-ee detectors are required, which will cost some money.
Dmitry Shatilov asked about a design with 4 IPs, but Katsunobu answered that it does not fit. Suggestion for tappering was made and Andreas Doblhammer will perform the study as well as checking the tracking with synchrotron radiation in MADX.
Anton suggested to ask for a tool in MADX for DA optimization. John Jowett answered positively and replied that cross checked can be done with the perturbative theory.
The BINP colleagues will leave and will come back at the end of September.
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