# Optics Measurement and Correction (OMC) – LS3 Planning Optics Measurement and Correction represents a critical activity, and key bottleneck, during LHC commissioning. To ensure machine protection and optimal performance, each operational configuration requires that a large array of optical parameters should be corrected to a high degree of precision, including: - beta* - beta-waist - beta-beat - horizontal dispersion - vertical dispersion - key phase advances - local linear coupling - global linear coupling - detuning - IR feed-down - nonlinear resonances The objective of this project is to support development of improved optics commissioning tools, to facilitate more efficient optics commissioning in preparation for the HL-LHC. ## Key objectives ### OMC model and response matrix generation - With the decision to end support for the MAD-X simulation code in Run4, OMC model generation for linear optics and response matrices should be migrated to Xsuite - Python functionality of new simulation codes should be utilized to support simpler on-the-fly adaptation of response matrix calculations ### Nonlinear optics measurement, correction, and automation - Develop tools to automate nonlinear optics scans, in particular: - RF scans - crossing-angle / orbit-bump scans - Develop improved response matrix generation tools for the nonlinear optics - At present NL-optics knob definition cannot be performed online - Utilize novel functionality provided by the MAD-NG simulation code to efficiently generate high-order response matrices - Develop improved analysis tools / GUI to support efficient post-processing of NL-optics measurements and calculate corrections, to supplant existing scripts and manual procedures ### Bad BPM identification - Develop improved tools to support automatic identification of problematic BPMs from: - raw data - spectra - outlier analysis online during optics measurements, which represents a necessary prerequisite to any future automation of measurement and correction - Develop improved tools for the long-term monitoring of problematic BPMs across the ensemble of optics measurements performed during a given commissioning / year / run, with a view to providing regular input to BI ### Automated excitation - Develop tools to improve efficiency of AC-dipole excitation (to be able to exploit any future AC-dipole upgrade increasing allowed kick frequency) - A first update to the LHC multiturn GUI to support a pre-programmed automatic kick program has already been developed; during the 2025/26 period these new tools should be tested and refined as required - The present tools utilize basic figures of merit to define kick amplitudes; this should be updated with online action calculations to help ensure consistent measurement quality - Introduce automation of on/off momentum kicks into the program to facilitate dispersion measurement ### Towards automatic beta measurement - Complementary to improvements in automated excitation, develop tools to help facilitate non-expert linear optics measurement in the LHC - Online models should be automatically generated based on extracted optics present in the machine at the time of automated kicks performed via the multiturn GUI - A similar process is utilized already for basic models during ADT-based coupling measurement - For beta- and dispersion measurements models must be extended to include extracted knob settings (for example crossing-angles, spurious dispersion knobs) - Extend the multiturn application to automatically process coupling and optics measurements generated following completion of the automatic kick program - Develop improved software to support K-modulation measurements, including: - updates of the K-modulation tools and procedures to be compatible with HL-LHC circuits - developments of the OMC GUI to improve the pipeline between K-modulation measurements and optics corrections These developments are underway and should be tested during Run3 and refined as necessary ### Towards automation of global corrections - Study the possibility to shift basic global corrections of the linear optics to a non-expert task - At present the response matrix and global correction approach do not automatically account for circuit current limits - Integrate circuit limitations into determination of the global corrections - The global correction is in principle straightforward to define; in practice however, correction usually involves: - testing multiple predicted corrections in simulation - varying a selection of response matrix and measurement cuts - tailoring weighting between different optics parameters and measurement sources Study the viability of automating this process ### Local IR error corrections - Development of segment-by-segment tools for local error correction in the LHC IRs is underway within the framework of the OMC3 GUI - These tools should be tested and exploited during the remainder of Run3 - Action-Phase-Jump correction methods should be fully implemented in OMC tools to provide a complementary correction method to SbS - ML-based tools for IR error identification have been developed during Run2/3 - These should continue to be tested with a view to further integration in the OMC toolset - Provide a complementary correction method to SbS and APJ ### Local arc error corrections - Develop OMC segment-by-segment correction tools / GUI, together with support for automatic matching of: - orbit bumps - sextupole strengths to identify local arc corrections in a time-efficient manner ### Energy error identification / corrections - Analytical tools to support efficient optics correction due to energy offsets during the commissioning process are in development - These approaches should be tested and validated during Run3 ### Single pass dispersion - Develop OMC tools and GUI to support non-expert checks of single-pass dispersion in the LHC ### ADT-based measurements with nominals - Test OMC tools and methods with the transverse damper, to explore the viability of routine linear optics measurements with lumi-production beams ### Extension of OMC tools in the injectors #### SPS - Develop model creation tools for SPS (in line with those already existing for PSB, PS, LHC, and external machines) - At present coupling and RDT calculations in OMC tools are incompatible with SPS turn-by-turn data - Update OMC codes to facilitate coupling measurements with single-plane BPMs - Ultimately target development of routine coupling measurements in SPS using the ADT - Update existing LHC analysis tools for nonlinear optics to work in SPS - Notably amplitude detuning calculation via the OMC GUI in SPS requires implementation of corrections for un-kicked tune drifts (as already implemented in LHC) #### PS, PSB - Long-term turn-by-turn data acquisition in PSB and PS has so far been performed by logging of raw sum / difference signals from the BPMs via dedicated scripts provided by BI - These are then calibrated and converted to work with the OMC tools - Improve the pipeline between turn-by-turn acquisition and OMC analysis tools in the injectors to facilitate non-expert use of OMC measurements throughout the injector chain ## Short / Mid term LHC OP-facing activities ### K-mod application - Fix ability to load / re-analyse historical measurements in the GUI - Change information output by K-mod GUI: - clearly display beta* - beta-waist - waist values of the two beams - In results panel estimate separation of the two K-mod solutions (to help spot online issues with VdM analysis when L* approaches beta*) - In the GUI input explicitly display expected units for initial guesses of the beta* and waist - Develop tool in K-mod or OMC GUIs to publish summary of K-mod results to the OMC elog - Review / change coordinate system for waist and beta* calculations to simplify online understanding of waists ### Multiturn application #### Automatic estimation of the coupling correction from multiturn - Run OMC3 coupling calculation automatically for every kick from the multiturn application (as done today for the ADT-ACD type measurements) - Publish effective global coupling knob correction to the elog alongside automatic kick entries #### Online action estimation - Run OMC3 action calculation automatically for every kick from the multiturn application - Publish to elog alongside applied kick percentages - Switch kick scheduling targets from [mm] to action #### Feed-back states in multiturn - Investigate whether it is possible to speed up automatic restoration of initial feed-back states - Separate sending of state configurations between the two beams #### On / off-momentum kick scheduling - Extend automatic kick scheduling in the multiturn application to include off-momentum kicks - Automatically vary RF-trims and feed-back states - Coordination of kick scheduling between the two beams #### Kick scheduling in the ramp - Extend multiturn kick scheduling to allow automatic measurement in the ramp - Select series of matched points: - sanity checks of expected time between kicks - retrieve automatically energy and optics associated with the matched points - scale kick strength according to expected rigidity - schedule kicks of both beams at appropriate times in the ramp - Enable online adjustment of kick targets during the process in case losses do not scale as expected #### ADT-ACD optics mode - Define requirements for MPP and interlocks to allow dedicated optics mode of the ADT to be utilized from the multiturn application - Implement option in multiturn to switch ADT between coupling and optics mode ### Automation of RF and Xing scans - Develop GUI / tools for automatic large range RF-frequency and Xing-angle scans to simplify NL-optics commissioning ## Short / Mid term PS OP-facing activities - Pre-LS3: continue benchmarking of OPERA / MAD models of PS-MU auxiliary circuits - assess cross-talk - normalization - MRP dependence of the circuit responses - Investigate surrogate / best-knowledge models of the PS circuits to improve tune / chroma control in PS - Support tests of emittance measurement via numerical deconvolution with zero dispersion optics in PS - if successful develop non-expert tools to support PS operation - Improve tools for inloading of PSB / PS turn-by-turn data - expand segment-by-segment tools to support calculation of measured optics functions at injector instrumentation - Implementation of Xsuite models into OMC3 for the injectors