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7th FCC-ee Optics meeting
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Europe/Zurich
6-R-012 (CERN)
6-R-012
CERN
Participants: Sandra Aumon, Michael Benedikt, Andreas Doblhammer, Bernhard Holzer, John Jowett, Luis Eduardo Medina, Roman Martin, Katsunobu Oide, Frank Zimmermann.
Optics Update with element-by-element radiation by Katsunobu Oide
For his lattice in SAD, the quadrupole length was increased from 0.6 to 3m in order to reduce the synchrotron radiation, affecting the DA. A local solenoid compensation was included and the 1m-2mm beta stars were implemented. The tunes were changed in order to avoid synchrotron resonances. The RF sections were improved -Ideas exist to set only 2 RF sections, and this is why Andreas Dobelhammer is looking at the tapering.
In order to optimize the DA strengths of the magnets are automatically tapered with the local energy of the closed orbit.
Katsunobu estimated roughly the radiation in the quadrupoles of the arc via simple analytical formulas. He could estimate the relative amplitude in momentum as a function of the synchrotron tune, the emittance and the longitudinal damping per turn. His estimations from formulas were in good agreement with tracking simulation with element-by-element radiation. John Jowett reminded that the loss in energy due to synchrotron radiation in the quadrupoles - in particular of the quads in the IPs - were a strong limitation.
The DA for on-momentum particles are improved (9->12sigma) for 3m length quadrupoles. However the advantages to have interleaved sextupoles at 175GeV disappeared due the radiation in the quads. Frank Zimmermann asked abou the local chromaticity correction. Katsunobu replied that it is still present but one of the merit is broken.
John Jowett added that they made a scan in synchrotron phase at the time of LEP to optimize the DA.
Katsunobu presented the IP solenoid scheme, and a residual coupling remains. Frank Zimmermann and Bernhard Holzer objected about the hard edge fringe field for the solenoid. Katsunobu said that he did not observed any problem on the emittance because of that.
Katsunobu presented the layout of his lattice, with 0.8m separations after the common RF section. Bernhard Holzer said we have to guarantee that the beams are centered before the separation of the two beams. The RF sections were revised: if the nominal strengths of quads are symmetrical in the common section, it matches to the optics of both beam. This scenario is compatible with the RF staging. With 2mm vertical beta star, the DA is better.
John Jowett proposed an injection scheme with "Golf club", in which the beam is injected out of the stable phase, but it exist a narrow band of phi_s for the stable injected beam.
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