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ArcHalfCellMock-up Meeting - Alignment and Stability #1

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Federico Carra (CERN)
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Notes of Meeting Arc Half Cell Mockup – Alignment and stability #1

11th July 2022

List of people attending the meeting:

F.Carra (chaiman), K. Artoos, J. Bauche, L. Baudin, C. Eriksson, M. Guinchard, H. Mainaud Durand, M. Timmins,

Slides of the presentations as well as video recording of the meeting are available in the Indico page related to the meeting (https://indico.cern.ch/event/1181154/)

Agenda:

  1. Introduction of Alignment and Stability issues (F. Carra)
  2. Opened discussion (all)

 

  1.  

Federico recalled that considering the alignment procedures is one of the deliverables of the mock-up project.  
“Supports and stages and access to the components should consider alignment procedures”

Federico showed the table of alignment requirement presented at the FCC week by Tessa Charles.

On top of the static alignment tolerances, Federico recalled the objective of “no vibration mode below 100 Hz”, mentioned by K. Oide at the 1st FCC arc half-cell meeting.
 

  1.  

Helene commented that the resources required for this project deliverable should be well defined, Federico commented that the pre-design of the stability and alignment system is in the scope of the mock-up project, therefore some design activities could be included in the design job under opening at the MME design office.

The alignment tolerances presented in Tessa table are “doable”, they have been achieved in synchrotrons.
But given the huge number of elements to be aligned in the FCC, simply scaling from what is done in synchrotron to FCC is unlikely: from 200 girders used in synchrotron to 1500 girders! That would take several years to align the FCC… Even if a beam-based alignment strategy is used, the “relative” alignment or smoothing “lissage” must be done.

The use of girders allows pre-alignment on the surface and ease the alignment in the tunnel. IF, the support is rigid enough, and if the elements are rigidly installed on that support, it would be no re-alignment of elements in the tunnel only alignment of the girder itself.

Using a girder could be a drawback for the frequency of the first mode, which would decrease with respect to a system without girder. Michael commented that, based on his experience on similar systems, a first frequency of 100 Hz seems impossible with conventional support or alignment systems.

 

Detailed stability tolerances must be defined :

  • On which range of frequency? Typically, integrated RMS values must be given for a defined frequency range.
  • On which magnet element? Dipole? Quadrupoles? Sextupoles?
  • Over which time?? That raises the question of thermal stability (this is more related to alignment, lower frequency)
  • Over which length ? (It is done over the length of one element) Are there requirements with respect to coherence length?
  • And for the booster elements?

 

Inspirations from other structures:

 

Ferromagnetic requirement on the support?
In general no, structural steel can be used. The support of the orbit corrector might be a particular case.

 

The stability issue must be addressed in early stage of FCC design to have time to implement modifications on Civil Engineering, or Cross-section organisation if needed.

 

A remote alignment system option was proposed in CDR. Tele-operated system relying beam-based alignment on sensors developed from HL-LHC is based on a monitoring and alignment system such as that proposed for the CLIC. This option has been discarded (for cost reasons?).

 

As a first step, the study of the components can be decoupled. In a second step, a study must be performed integrating all the modes of all the components. Vibrations can propagate through the ground, through beam pipes, through water cooling and powering connections.

 

Be aware of limitations and constrains:

  • Given the length of the FCC-ee cell and the accuracy required, the standard techniques of levelling and technologies are not scalable to FCC size.
  • Based on a lot of previous experience having the 1st mode of the support below 100 Hz is impossible! (Steel supports will be around few Hz, Cast support 40/50 Hz). LHC cryodipole have a transfer function with the amplification factor of 100, around 20/25 Hz.

Preliminary studies can be done based on current design of the supports to give boundary conditions and realistic values of vibration level based on reference ground acceleration, (and water cooling?).

Characteristics (weight and volume) of the supported elements must be gathered to prepare preliminary study in collaboration with  integration team and Antoine Chance for the Booster.
 

Actions follow up:

  1. Define an updated table of key requirement and parameters related to the design on the collider and the booster.
    This table should be based on CDR and updated following presentations given at FCC week. Discussion with Franck, Rogelio and Antoine Chance.

à Federico to trigger the action, and to crosscheck the tables with the stakeholders.

 

  1. Preliminary study based on existing design of the supports  à Lucie
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