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ArcHalfCellMock-up Meeting #10
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Europe/Zurich
Notes of Meeting Arc Half Cell Mock-up #10
28th November 2023
List of people attending the meeting:
F. Carra (chairman), J. Bauche, A. Chance, H. Gamper, M. Guinchard, P. Lersnimitthum, R. Losito, E. R. Howling, L. Hutin, K. Oide, A. Piccini, M. Timmins, F. Valchkova-Georgieva, F. Zimmermann.
Slides of the presentations are available in the Indico page related to the meeting (ArcHalfCellMock-up Meeting #10 (28 novembre 2023) · Indico (cern.ch)).
Agenda:
- General information on the Mock-up project (F. Carra)
- Booster circumference and position (F. Zimmermann, A. Chance)
- Presentation of the collider stability assessment (A. Piccini)
- Presentation of the booster stability assessment (L. Hutin)
1)
F. Carra introduced the meeting by reviewing the minutes and the actions of the last meeting. Concerning the action to find a girder, M. Guinchard confirmed that the action is in progress, but that finding a girder of this specific size is more complicated than expected. F. Carra added that if it is not possible, a marble girder can be bought from the market, it is probably not expensive. Regarding specifications, now that we know more about system stability, a discussion with K. Oide and T. Raubenheimer can be organized.
2)
F. Zimmermann presented one of the slides from A. Chance’s FCCIS workshop presentation. The request is to have the booster at a transversal position 20 cm more inwards with respect to the collider, to be able to better inject trains of bunches, in short times. K. Oide pointed out that this is not strictly needed, as it can be done also with different circumferences. F. Carra commented that the option can be investigated, but in the meantime invited the optics experts to further discuss about how stringent the requirement of same machines length is (action F. Zimmermann, K. Oide, A. Chance).
F. Carra also commented that the one slide presented by Frank touches several different points:
- Consistency of A. Chance’s booster path model and latest version of the integration models. A. Chance and F. Valchkova-Georgieva will check this together and make sure that the latest model is provided to Antoine (action A. Chance and F. Valchkova-Georgieva).
- This modification will have an impact on integration, for example if the booster support is moved to the other side of the collider, the space for transport is reduced. F. Valchkova-Georgieva will communicate with the “Technical Infrastructures” group and will propose an integration option (action F. Valchkova-Georgieva). M. Timmins and F. Zimmermann commented that, among the different options under current consideration by Fani, probably the one requiring less changes to accommodate this request is the mid-term review version with the booster supported on the ground, which (we will see later today) is also the more stable.
- The impact in terms of radiation also needs to be studied, to be discussed with A. Lechner and B. Humann (action F. Carra).
3)
A. Piccini presented the numerical methodology developed to assess stability at the magnetic axis of the booster and collider. As well as more detailed results on the parametric study of collider stability, thus offering an optimal girder solution in terms of stability. It is important to note that:
- the numerical methodology currently only evaluates the impact of ground motion on the structure but does not assess the impact of forced excitation and crosstalk (currently being studied).
- with this method, stability is assessed at the level of the magnetic axis, but specifications are given at the level of the beam axis! And the transfer function between the two will not be equal to 1.
- with just the high envelope of ground motion (LHC level), the specifications are not met.
- the aim of this study is to compare different solutions in terms of stability rather than to determine the actual stability value.
R. Losito asked what would be the impact on results if the input were to change? For example, FCC ground motion instead of LHC ground motion. A. Piccini explained that even if the FCC tunnel will be deeper the cultural noise is attenuated on the first layers of the ground, and M. Guinchard added that once in the molasse the attenuation of the vibration will be limited. R. Losito commented that the question is more about how much we are sensitive to the ground inputs in the qualitative evaluation of the different options: if the input changes, are the same qualitative conclusions valid? F. Carra commented that the response is given by the transfer function so, unless the relevant excitation frequencies change a lot, the better solution should remain the better independently of the input (this is maybe less true in case of forced excitations such as ventilation, vacuum pumps, etc. but we are not at that stage of evaluation yet).
K. Oide asked why do we need a girder when it affects beam stability? J. Bauche answered that it is mainly due to the vacuum chamber, which is common to the quadrupole and sextupoles, with a girder assembly can be carried out on the surface whereas without it everything would have to be installed in the tunnel. This is not possible because it requires split magnets that cannot be precisely assembled after chamber insertion in the tunnel environment. F. Carra added that further studies have been carried out to determine the usefulness of the girder and these documents can be forwarded to him for further explanation (action F. Carra and A. Piccini).
F. Carra concluded that M. Timmins and C. Tetrault will provide to Fani the latest version of the girder, determined by these calculations, to be included in the integration drawings, and to verify that it does not pose integration issues (action M. Timmins, C. Tetrault, F. Valchkova-Georgieva).
4)
L. Hutin presented detailed results of the stability study of three possible booster geometries (Centered with respect to the collider, shifted with respect to the collider and ceiling mounted). It has been highlighted that the ceiling-mounted geometry performs in terms of stability far worse than the grounded ones (which behave similarly).
F. Carra asked if it would be possible to run a simulation again, shifting the booster by 20cm as discussed at the beginning, to see the impact in terms of stability: this will deteriorate stability, but by how much? (action L. Hutin).
Actions follow up
- F. Zimmermann, K. Oide, A. Chance will invite optics experts to further discuss about how stringent the requirement of same machines length is.
- A. Chance will check with F. Valchkova-Georgieva whether the booster layout used for these calculations is the latest one.
- F. Valchkova-Georgieva will communicate with the “Technical Infrastructures” group (Done during Technical Infrastructures Coordination meeting #53).
- F. Valchkova-Georgieva will study an integration option for the shifted booster within the Technical Infrastructure Working Group, and the Mock-up team can contribute to this with mechanical studies.
- F. Carra will discuss with A. Lechner the impact of shifted the booster in terms of radiation.
- F. Carra and A. Piccini will forward the documents concerning the girder study to K. Oide.
- M. Timmins and C. Tetrault will provide to Fani the latest version of the girder.
- L. Hutin will run a simulation again, shifting the booster by 20cm.
Opened actions
- F. Carra and A. Piccini will organise a meeting with T. Raubenheimer and K. Oide to discuss about the specifications. (Meeting #7)
- The MME team will find an available marble girder to pursue the measurements. (Meeting #9)
- M. Guinchard and D. Thuliez will evaluate the transfer functions following the measurements. (Meeting #9)
Minutes written by: Audrey Piccini
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