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115th Impedance Working Group meeting

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774/1-079 (CERN)

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Carlo Zannini (CERN)
115th Impedance Working Group meeting
Zoom Meeting ID
68697324208
Host
Elena Macchia
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Date: 03/06/2026

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  • Thermo-mechanical assessment of SPS-BGI with new simulation model (SY-BI - C. Pasquino, J. Storey)
  • Reviewing ferrite design for CPPS Roman Pots based on thermo-mechanical considerations (CMS - M. Delie)

 

Present: W. Andreazza, C. Antuono,  G. Banks, G. Bregliozzi, S. Calatroni, M. Deile, G. Favia, E. De La Fuente Garcia, D. Gibellieri, A. Grudiev, A. Huber, I. Karpov, P. Krkotic, K. Lasocha, E. Macchia, L. Margerison, N. Mounet, M. Neroni, C. Pasquino, S. Redaelli, J. Sonpar, J. Storey, I. Valencia Ruiz, C. Zannini

E. de la Fuente Garcia, J. Sonpar: Impedance and power loss map of SPS BGI
Discussion:
James asks something can be done to change the design,  Elena replies that for now they work with the design as it is, but it's possible to iterate with the materials; optimizing the model is going to be much easier now that the setup exists. 
Chiara Pasquino asks about the modes leaking through the grid and Elena replies that the third mode is the one leaking, but it's not concerning since the total power it contributes with is not high. 
James asks about the shield, Julian says that the one with 1 mm holes was used (not the diamond-shaped grid). James asks if it is possible to simulate both grids to check the difference. Elena replies that Valentina Daliento (Carlo's student) is working on this.
Alexei asks what is the actual power loss on the feedthrough that contributes to heating. Elena replies that all metal losses are going to the NEG coating (nothing to the stainless steel); what is computed is out of the feedthrough. Elena clarifies that the metal losses on the NEG coating are wall losses. Regarding the power loss analysis per material, Elena clarifies that the power is not scaled to the SPS beam, and it is only used to compute the percentage.
James asks if the simulation includes the thickness of the NEG and the surface resistance. Julian replies that it was taken into account in the old model and it can be studied again for the new model. 
Michela adds that there are measurements foreseen in the EMC lab on the BGIs, and wire measurements for the impedance could be added.

 

M. Neroni: Roman Pots
Roman pots were already discussed in the #112 IWG meeting, Michela today adds study on the contribution to the effective longitudinal impedance. The overall impedance budget remains unchanged. Michela asks Mario for confirmation that the total number of Pots will not change in Run 4 with respect to Run 3.
Discussion:
Stefano asks if there is a clear limit on the number of roman pots, since it is possible that another two will be added in Point3. Michela answers that adding more roman pots can have a substantial contribution towards the instability limit (on the longitudinal plane), since it is already 5-6% (in collision) with 6 pots per beam. Carlo adds that in the transverse plane this is less critical. Stefano concludes that any additional request then needs to be studied and Michela agrees.


M. Deile: AoB: comment on PPS2
Discussion:
Mario asks if it is a problem to segment the ferrite in 24 instead of 6. Michela says that according to her it should not affect impedance mitigation properties, unless other changes in the geometry are made. Carlo adds that it is not something that can be checked in simulation, and measurements should be made since it is more of a mechanical consideration.
Gabriel asks if there are requiremets on the self alignment. Mario says that they are fixed so there should not be an issue. 
Alexei asks if the ferrite can go through the brazing temperature-wise and Mario says that it can. Alexei adds that this geometry is already used in other absorbers and there are techniques other than brazing that can be adopted.
Discussion on the fact that no changes in the geometry can be made, only the addition of a copper ring to improve the contact (also a copper spring considered). Copper coating is also something to be tested, Giorgia says that it was already tried by them and the thermal conduction coefficient is very high in their case.
Carlo summarizes asking if they will go ahead with the segmentation, Mario says that it is not yet decided and he would prefer not to do it.


C. Zannini: BGC Beam 2
Carlo proposes to present the impedance assessment overview table in one of the next IWG meetings, since there is going to be an ECR about it.

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