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Optics MDs requests
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6/R-012 - conference room (CERN)
Optics MDs requests
Meeting on Optics related MD requests
News / Introduction
Rogelio reports that an LSWG meeting with a busy agenda is scheduled on February 20 (in the Geneva school holiday week, such that some people including Rogelio cannot attend). The HL-LHC optics related requests in that meeting will be presented by Riccardo. As evident also from this meeting, there are many ideas for interesting studies with importance for future LHC operation and in particular the HL-LHC. The current LHC draft schedule for this year has the first two MD blocks in May and June (maybe also during commissioning). The available MD time is limited. It is important to plan the MDs efficiently, profiting from synergies with other studies and in particular collimation developments including ion optics, and to consider to also profit from commissioning or use parasitic MD time when possible.
HL-LHC Optics MDs, Riccardo, slides
Riccardo presents an overview of planned HL-LHC optics related proposed MD studies, based already on preparatory discussion with several colleagues. Even if the full potential to minimize beta* in IP1&5 requires the new triplets, there is much that can be learned with present LHC for HL-LHC and important to guide outstanding decision on crossing plane changes, beta* and ATS steps. Priority will be on new studies checking limits in extreme cases and extending in several cases beyond HL-LHC design report : modified optics for in points 3, 7 to optimize collimation and impedance including ramp and squeeze, optics with increased ATS factor (up to 6.6) and lower beta* down to 7.5 cm in the non crossing plane and optimal choice of beta* and ATS factor when collapsing bumps (going into collision). The proposed 2024 MDs with focus on using pilots and one nominal bunch (for synergies with beam-beam studies).
Collimation MDs on optics, Björn Lindström, slides
The collimation and optics related proposed MDs can be subdivided into three groups.
The first is on improving the IR7 optics to reduce the collimator induced impedance and improve the cleaning performance. This was already planned in detailed and schedule for 2022/2023 but could not be done because of beam unavailability.
The second group of studies aims at optimizing IR7 during the ramp and de-squeeze/squeeze. These studies could be combined with more general HL optics MDs and may also be useful for the current LHC to reduce loss spikes in the ramp.
The third group is on improving IR3 optics to further reduce impedance, re-balance IR3/7 losses and optimize collimation performance. These studies may require a desqueeze during the ramp.
OMC MD requests, Ewen, slides, Tobias Persson, slides
Ewen gives a comprehensive overview of OMC (optics measurement and correction) requests and ideas. There are a number of (6 - 7) requests from previous years including the study of 60 degree optics, corrections in presence of failing correctors, a study of amplitude dependent beta-beat and dynamic changes of resonance driving terms. Some of these studies could be done parasitically or during commissioning. He shows that in addition there is a lot of potential for further interesting new studies (measure arc errors, IR sextupole and feed-down, detuning degradation) and open questions.
Tobias discusses why (aging/failing by radiation) and how to perform missing corrector studies. He presents a new idea for studies based on cogging (adjusting the RF-phases to move the collisions longitudinally). This could be used to measure the beta-waists in the IRs, that has been difficult in the past and will be even more difficult (and important) for high-luminosity. The minimum waist position can be different for the two transverse planes. Using cogging and different bunch intensities, the new idea has the potential to determine the optimal waist positions and in addition to measure emittances. Tobias says that the LHC is currently pre-cycled for ~ 30 minutes each time when power convertors go to standby for local access, which may happen rather frequently (like twice a week), and says it remains to be checked to which extend this is needed.
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