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FCC-ee tuning simulations and solenoid modeling
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Videoconference
FCC-ee tuning simulations and solenoid modeling
- Zoom Meeting ID
- 69935059478
- Host
- Rogelio Tomas Garcia
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10/11/2021 LNO meeting on FCC-ee tuning simulations and solenoid modeling
News and round table :
Last week we had the joint NDC-LNO meeting https://indico.cern.ch/event/1091566/
reviewing the LHC beam test and discussing the ULO observation, now known to be caused by
a buckled RF finger in the interconnect QQBI.21L3. It was decided to warm-up sector 23 and to replace the compromised plug-in-module, pushing the start-up of Run 3 well into March 2022.
Based on the observations in the LHC test, Elena and Tobias will prepare a list of potentially bad BPMs to be communicated to the beam instrumentation group.
Ewen continues the work on optics measurements for the injectors and will present at the Montreux workshop.
There have been discussions with Tessa Charles working for the main FCC-ee ring, Simone Luzio from ESRF, and Barbara Dalena working on the FCC injection booster resulting in an interest to work together on a common modular code base for optics tuning studies.
Rogelio says a meeting is planned between students and the ABP group leader, aiming at identifying and minimizing any possible issues under the current (COVID) working conditions. Tobias said it would be interesting to pass on the conclusions of this meeting to the student supervisors.
Alex Huschauer says that this week is the last this year with injector operation with a peak in MD-requests,
including a study by Wietse to minimize the dispersion at the wire scanner. An issue with crosstalk between cycles was identified and fixed.
The LIU goal of 2.6e11 particles / LHC bunch was exceeded reaching nearly 3.e11 particles.
Tobias reported on recent updates for MAD-X. For details see his slides.
The output of the EMIT module can now be saved as table and written as tfs file.
Piotr has connected spin from PTC to MAD-X.
Several smaller issues have been identified and fixed with the help of external collaborators J. Scott Berg, T. Glässle and Y. Levinsen.
Rogelio asks when the next MAD-X version will be released. Tobias says that discussions continue on how to misalign the wire using similar conventions as SixTrack.
This meeting had two presentations with slides prepared for the CPECws2021 international workshop https://indico.ihep.ac.cn/event/14938/ this week.
FCC-ee tuning simulations, Tessa Charles, slides
Tessa presents an update of her misalignment and correction studies for FCC-ee.
She shows a table of the random errors that were included in the studies and shows the results obtained after tuning for the recent 4IP ttbar (182.5) GeV sequence. The studies are rather time consuming and a speed optimization and access to more computing resources would help. She presents a list of further effects to take into account including solenoid and tapering imperfections and the simulation of optics measurement and correction techniques. Studies for smaller machines including light sources use the LOCO code, but appear according to Tessa to be too slow for the large FCC-ee. Katsunobu Oide proposes to still try to use LOCO starting with a reduced number of correctors to increase speed.
Rogelio announces that a FCC-ee tuning meeting will take place on the 17th: https://indico.cern.ch/event/1097453/ to further discuss the open points with other collaborators.
FCC-ee solenoid modeling, Helmut Burkhardt, slides
Helmut reminds that the 2T detector solenoids are the strongest magnets in the lattice, and that their impact on the beam dynamics is generally small but non-trivial to take into account accurately. The detailed modeling uses numerical methods based on tracking with GEANT4 or his dedicated FieldStep code, using currently an analytical B(x,y,z) field, to be replaced later by measured field maps.
He argues that the canonical coordinates used by codes like MAD-X are based on a Hamiltonian approach, that can easily be translated to real space coordinates (x, x',..) as long as the vector potential components Ax, Ay remain at zero. This is the case in field free regions or for standard lattice magnets like quadrupoles or multipoles, but not for solenoids that have major nonzero Ax, Ay components depending on the position in the magnet. By tracking using the detailed field information with and without small offsets, he determines numerically the transport matrices for real space coordinates step by step. The resulting matrices have a determinant = 1, but are generally non-symplectic within the solenoid, as also noted by Talman in his LNP343 lecture notes. Technically it could be possible to use directly the numerically determined, locally non-symplectic matrix slices in MAD-X with the sympl=false option, with however currently unknown consequences on TWISS and EMIT.
Helmut observes, that the FCC-ee beam divergence is small compared to the crossing angle. The main effect of the solenoids can be taken into account by just using orbit correctors. With this fully symplectic approach, he reproduces the orbit, dispersion and energy loss determined with tracking. As a next step he proposes to include the remaining small coupling and focusing effects based on the known symplectic solenoid maps. When done, he proposes to make the sliced IP sequence available for tests that should be possible using standard MAD-X.
The next meeting could be devoted to codes, possibly organized as in person meeting in the BE auditorium.
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