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103rd Impedance Working Group (new crystals in the TECA)
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Europe/Zurich
774/1-079 (CERN)
Present: Hikmet Bursali, Sergio Calatroni, Tristan Calvet, Luigi Esposito, Giorgia Favia, Elena de la Fuente, Marcel Himmerlich, Michael Howes, Patrick Krkotic, Nicolas Mounet, Michela Neroni, Leonardo Sito, Christine Vollinger, Carlo Zannini.
ACTION for new optimized crystals in TECA (IWG): to perform impedance simulations with new crystals and RF screen for circulating ECR.
ACTION for LESS treatment: topic to be followed up with Lotta for e-cloud.
ACTION (IWG): to provide with a comment for the ECR on LS4 upgrade of vacuum configuration in experiments.
Installation of new optimized crystals in the TECA – Luigi Salvatore Esposito
Luigi introduces the necessity for installing a new set of crystals: motivated by the BDF/SHiP experiment that requires four times larger POT and therefore losses need to be reduced by the same factor. The talk focuses on the SPS assembly. Luigi mentions the production chain of bent crystal devices and the expected deliverables. He mentions that the ECR will circulate soon.
Luigi shows the installation in LSS4 in SPS and he mentions that the device was presented in IWG meeting #48.
- TECA principle remains essentially unchanged
- The present crystal will be replaced with a crystal array MVRA (baseline change) and an Optimized Single Crystal.
The new crystal holder is larger, therefore the RF screen will have larger openings to accommodate for it. The operating position will be 10-15 mm from the beam. During operation the crystals are in parking position and when operating the only one crystal is protruding while the other one remains close to the parking position (moving a bit towards the inside as well).
Discussion
Christine asks if the openings on the RF screen are already optimized to have minimal aperture. The openings need to be as small as possible to allow only minimal coupling. Luigi answers that this was done.
Carlo and Christine ask for the 3D model that can be used for simulations. Tristan and Michael will share the model with the IWG. Tristan also asks to have information on the heat deposition, if possible.
Luigi asks for the timeline on the impedance simulations. The ECR needs to circulate soon, so there is the urgency to get an answer.
AoBs
Updates on the Q5 standalone magnets laser processing (Patrick Krkotic)
During Run2 strong e-cloud losses in IR1/5, baseline solution is amorphous carbon coating and as alternative solution some laser surface treatment was proposed.
Some studies were already presented in IWG97 and 100 meeting. A remaining question was on the mitigation of e-cloud in BPMs and closed orbit dipole corrector.
Patrick mentions a presentation by Lotta at the WP2/WP13 meeting. Main messages:
- for BPMs there is low risk of e-cloud
- for the correctors the e-cloud is dependent on the corrector field, so there is a moderate risk.
Patrick did some studies on the orbit correctors beam screens. He shows the increase in the real longitudinal impedance for the horizontal and vertical configurations treated with LESS.
Discussion
Marcel mentions that the options will be presented in a meeting later this year and the ECR will probably circulate in October.
Nicolas asks if the laser treatment is planned on the full length of the lateral curved surface. Marcel mentions that this will be adjusted based on the simulation on the e-cloud.
Follow up on IWG recommendations for experiments vacuum system configurations in Run 4 (Patrick Krkotic)
Patrick mentions that for LS4 upgrade in the experiments the ECR will circulate soon and a comment from the IWG is expected. Information can be found in TREX meeting: https://indico.cern.ch/event/1543046/
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