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108th Impedance Working Group (TCLD, SPS BGI, LHC BWS)
Minutes of 108th Impedance Working Group Meeting
Present: Oliver Aberle, Chiara Antuono, Sergio Calatroni, Elena de la Fuente García, Miguel Díaz Zúmel, Giorgia Favia, Dora Gibellieri, Antonia Huber, Patrick Krkotic, Leon Kronshorst, Elena Macchia, Chiara Pasquino, Hermann Pommerenke, Benoît Salvant, Leonardo Sito, Julian Sonpar, Harry Sullivan, Christine Völlinger, Carlo Zannini.
Excused: Nicolas Mounet
TCLD impedance studies (Chiara)
RF-shield of SPS BGI (James Storey)
The SPS BGI has shown communication problems due to RF interference coming from the beam.
A succession of RF-Shields were developed to try solving this issue:
- An initial RF-Shield #1 (Diamond) was introduced, but did not work correctly with AWAKE beams and with high intensity LHC beams.
- Afterwards, the RF-Shield #2 (Block with 1mm⌀ holes) was implemented, together with the addition of a sealing plate. This successfully mitigated the RF interferences from the beam. However, it has a low signal yield due to the small holes.
- Finally, the RF-Shield #3 (Hex pattern with 1.2mm ⌀ holes) still mitigates the RF interferences from the beam, and should have a good signal yield, thanks to the increased radius of the holes. The number of pixels per column increases and is now good enough.
Conclusions
- New, final shielding has 1.2mm ⌀ holes
- It is still unsure what mitigated the RF interference from the beam. If it’s the new sealing plate, then we could go back to the diamond shield (#1).
- Would impedance matching on the HV port improve the situation?
Discussion
- James asks if an improved contact between the diamond grid and the plate could be beneficial
- People are divided about whether or not they should come back to the diamond shield
LHC BWS – Change of card positioning (Harry Sullivan)
The parking position in the new wire scanners for the LHC must be changed, with respect to the initially foreseen. The reason is that the fast side of the motor must be at the parking position. To achieve this, the top part of the WS will be rotated 180 degrees.
The impact of the change is that the conductive tracks will then face the beam. Michela computed the impedance after the change, and the impedance impact is judged negligeable.
Discussion
Harry says that they did not want to also rotate the tank, since it has already been measured by metrology.
Chiara P reminds that this is the first prototype.
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