Choose timezone
Your profile timezone:
21th FCC-ee Accelerator meeting
→
Europe/Zurich
6/R-012 - conference room (CERN)
Minutes from the FCC-ee Accelerator Design meeting of 2 November 2015
Participants: Sandra Aumon, Bastian Haerer, Mike Koratzinos, Katsunobu Oide, Pavel Piminov, Sergey Sinyatkin, Frank Zimmermann
Remote participants: Alain Blondel, Yunhai Cai, Mauro Migliorati
0) Comments on the minutes of the last meeting
There were no comments on the minutes from the previous meeting (5 October 2015)
1) Dynamical aperture comparison
Yunhai Cai presented a comparison of two lattices, from K. Oide (asymmetric) and A. Bogomyagkov (symmetric design). The code used is LEGO. There are several tracking versions. The results shown are for thick elements (piece-by-piece Hamiltonian solutions). The beam energy is 175 GeV,
-
Alain Blondel asked about the effect of radiation damping. Yunhai Cai replied that the effect is opposite on momentum and off momentum, as he should show now.
-
Katsunobu Oide commented that he beta*’s are different for the two lattices, perhaps not taken into account.
Momentum is about 1% or 1.5%, respectively, without radiation damping. Momentum acceptance increases to 2% for K. Oide’s lattice. A. Bogomyagkov’s lattice is not completely optimized for dynamic aperture.
-
Mike Koratzinos inquired why 1% aperture has a slightly larger aperture than 0.
The tracking results roughly agree with Katsunobu’s results.
-
Katsunobu Oide commented that his results are slightly worse, which might be due to the inclusion of fringe fields in his tracking.
-
Alain Blondel remarked that the vertical dynamic aperture is larger for Anton Bogomyagkov’s lattice and asked whether this could support a larger beam-beam tune shift. Yunhai Cai replied that this is likely to be the case.
Yunhai Cai presented a Taylor expansion for the tune shift. The tunes of the two lattices are different, and so are the detuning terms. K. Oide’s lattice operates close to the integer. The horizontal amplitude detuning is smaller for K. Oide’s design. The chromatic behaviour is better for A. Bogomyagkov’s lattice.
-
Katsunobu Oide is further optimizing the momentum acceptance of his lattice.
Yunhai Cai presented dny/ds as a function of s. For K. Oide’s lattice the asymmetry and large local chromaticity in the arcs are visible. The W functions show a similar behaviour.
-
Katsunobu Oide had corrected the local chromaticity in the RF sections.
The second and third order dispersion functions show similar behaviour.
Several conclusions can be drawn. Momentum aperture is larger than 2% with radiation damping and tapering. The symmetric solution has a better chromatic optics, but it has higher critical photon energy
-
Frank Zimmermann asked whether quantum excitation has been or could be included. Yunhai Cai replied it was not, but could be done. Katsunobu Oide commented that Demin Zhou had performed tracking with quantum excitation with unclear conclusion.
-
Alain Blondel inquired about the difference in the chromatic behaviour. Yunhai Cai replied that the tune also plays role in this behavior.
-
Mike Koratzinos asked whether negative momentum offsets could also be included.
-
Katsunobu Oide remarked that tracking at the IP should include the effect of the crab waist sextupole.
2) Nonlinear Dynamic Study of Oide’s FCCee
Pavel Piminov discussed a check of K. Oide’s lattice from 13 October 2015. Dynamic aperture for 1000 turns without synchrotron radiation shows gaps due to synchro-betatron resonances. Dynamic aperture results were shown for different energy offsets. The same results were presented for 45.5 GeV.
-
Katsunobu Oide commented that the results also roughly agree with his.
-
Pavel Piminov remarked that he could include a global damping, but not element-by-element damping.
3) IR magnet design
Mike Koratzinos discussed the first steps of the IR magnet design. He described he problems, the steps already made, and further steps. The contributions from several BINP, CERN and LBNL colleagues were acknowledged.
The IR design comprised 4 or 5 magnetic elements. Objectives include the minimization of the vertical emittance growth. Objective no. 2 will be to minimize the cross talk between the final-focus quadrupoles. One constraint is not to go beyond 100 mrad. The emittance growth is larger at lower energy.
The dispersion was calculated from the field map (computed with a program “FIELD”) and looks consistent with a calculation by Sergei Sinyatkin. The solenoid set up was described in great detail. The magnetic field was calculated along the path of the electron. Components from curly-H were analysed. The emittance blow occurs mainly at the second edge. The number agrees with Sergey Sinyatkin’s to within better than 20%. Ike Koratzinos added a third coil to smoothen the transition. The emittance growth is reduced by a factor of two, to 0.1 pm per two IPs.
Small changes can have a large effect on emittance.
The work plan is to understand the emittance blow up and afterwards to look at the quadrupoles starting with double=helical magnets.
-
Frank Zimmermann asked how the strength of the third solenoid was adjusted. Mike Koratzinos replied that he matched the dispersion to zero at the outside point.
-
Frank Zimmermann inquired whether there are other constraints from polarization and coupling.
-
Alain Blondel remarked that the integral of the solenoid should be zero. Eliana Gianfelice could check the higher-order effects due to synchrotron radiation, using a spin tracking code.
-
Mike Koratzinos commented that the outer edge of the third solenoid is at 105 mrad, without cryostat. Alain Blondel suggested checking the size of the solenoid with the magnet experts.
-
Mike Koratzinos commented that the emittance-growth contributions from the rest of the ring and from the IR to the vertical emittance have to be added. A 0.1 pm value from the IR (sum of two IPs) looks acceptable for a target emittance of 1 pm.
There are minutes attached to this event.
Show them.
