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presented by L. Bottura Workshop CERNmonix XIV Thursday, January 20 th , 2005

RMS forever !. Hasta la victoria, SIEMPRE. How the Magnetic Measurements and the Reference Magnet System (RMS) will be used for commissioning ?. presented by L. Bottura Workshop CERNmonix XIV Thursday, January 20 th , 2005.

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presented by L. Bottura Workshop CERNmonix XIV Thursday, January 20 th , 2005

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  1. RMS forever ! Hasta la victoria, SIEMPRE How the Magnetic Measurements and the Reference Magnet System (RMS) will be used for commissioning ? presented by L. Bottura Workshop CERNmonix XIV Thursday, January 20th, 2005 Special thanks to JPK for his fervor, persistence, and faith in reference magnets

  2. Outline • Summary of information available on day-1 from magnetic measurements at: • warm • cold • Injection setting and ramp generation (currents) in: • main circuits (MB, MQ) • corrector circuits (MCS) • The RMS conceptual design and results of the review • RMS concept proposal • work in progress • Open issues and conclusions

  3. warm measurements on the production: all (superconducting) MB, MQ, MQM, MQY: main field integral strength higher order geometric harmonics all (superconducting) MBX, MBRx, MQXx warm measurement on MQTL so far at CERN most (superconducting) lattice corrector and spool pieces (about 90% of data available) all (warm) MQW a sample (5 to 10) of other warm insertion magnets (MBXW, … measured at the manufacturer before delivery) at the present rate, cold measurements on: ≈ 20 % of MB and ≈ 20 % of MQ in standard conditions special tests (injection decay and snap-back, effect of long storage) on 15…20 MB a sample of MQM and MQY (10 % SM-18, 30 % B4) ≈ 75 % of MBX, MBRx 100 % of MQXx (Q1, Q2, Q3) 2 MQTL cold tested (plan for series TBD(*)) a limited sample of lattice correctors and spool pieces (about 120 tests over 7000 magnets, plan for the series TBD(*)) Available data (*) see the next talk, by W. Venturini

  4. W/C CM offset geometric saturation W/C CC offset magnetization decay What data is stored ? example of integral dipole and sextupole field in an LHC dipole cold data a break-down in different components is necessary to accurately model the data

  5. higher values higher variability higher uncertainty smaller values smaller variability smaller uncertainty The field model • general decomposition in error sources, with given functional dependency on t, I, dI/dt, I(-t) (see appendix) • geometric Cngeom • DC magnetization from persistent currents CnMDC • iron saturation Cnsaturation • decay at injection Cndecay • snap-back at acceleration CnSB • coil deformation at high field Cndef • coupling currents CnMAC • residual magnetization Cnresidual • linear composition of contributions:

  6. If we keep going as we do today, by end 2006 we will have ≈ 3.5 million measurements and 35 GB of accumulated data in the databases… … what are we going to do with them ? The burning question…

  7. Use of data • The data will be used to: • set injection values • generate ramps • forecast corrections (in practice only for MB’s or IR quads) on a magnet family basis • Families are magnet groups powered in series, i.e. for which an integral transfer function (and, possibly, integral harmonics) information is needed. Example: the MB’s V1 line in a sector (154 magnets) • The concept is best explained by practical examples • MB injection settings • sextupole correction forecast from MB data

  8. MB injection settings - 1/5 • Determine the current I in the MB to obtain a given integrated field B dl over the sector (as specified by LHC control system). Algorithm: • retrieve warm transfer function TFWM for each magnet in the sector • apply warm-cold scaling fTF and offset DTF(I) and obtain the cold transfer function TFCM TFCM(I) = fTF TFWM + DTF(I) • integrate the TFCM over the sector TFC(I) = ∑M TFCM(I) • compute the current by inversion of the (non-linear) TFC I = (TFC(I))-1 B dl only if cold data is missing

  9. Warm and cold magnetic data is stored in an Oracle databases (todayin 3 different databases) containing separate entries for: warm data cold data injection flat-top warm/cold offsets injection flat-top components in cold conditions geometric persistent currents decay and snap-back saturation MB Injection settings - 2/5

  10. MB injection settings - 3/5 • warm/cold correlation based on production accumulated so far. • computed in July 2004 on approximately 100 magnets • offsets are stable, standard deviation acceptable and comparable with expected measurement accuracy fTF = 1.00 (-) DTF = 5.5(6) (mT m/kA)

  11. MB injection settings - 4/5 • The magnet installation sequence is determined at the Magnet Evaluation Board (MEB), based on constraints on: • geometry • field quality • other (quench, non-conformities, …) • The information is collected in an installation map, recorded in the Manufacturing and Test Folder (MTF) We know which magnet is where we can build integral field information

  12. MB injection settings - 5/5 • average transfer function at injection for sector 78 (extrapolated from 109/154 magnets allocated) • warm/cold extrapolation for 44/109 magnets (65 cold measured) TF1 = 10.117(5) (T m/kA) TF2 = 10.117(1) (T m/kA) • current in sector 78 for an injection at 450 GeV from SPS (1189.2 T m) I = 763.2(5) A Note down this number for sector test with beam !

  13. from fit of a sample of cold measured magnets from cold measurements Modelling functions for harmonics (see appendix for details) • geometric multipole • persistent currents • decay • saturation

  14. Sextupole forecast - 1/2 • compute integral of cold components over a sector as: • derived from measurements taken on each magnet, or • extrapolated from the average over magnets of the same family, e.g. • scale the function that describes the behavior of the component by the integrated value of the component in the sector, e.g.: • add all contributions • send the forecast to the LHC control system for correction (MCS and/or MS)

  15. Sextupole forecast - 2/2 error ≈ 0.2 units during the energy ramp

  16. Objectives: provide settings and trims in the main magnets (MB, MQ, …) and in the corrector circuits to prepare the LHC for injection, correct for decay and snap-back, program the ramp provide a display of the magnetic state in the main magnets (MB, MQ) play/replay machine cycles to prepare for a change of operating mode Review of the conceptual design (July 2004) MARIC presentation by R. Ostojic (August 2004). LTC presentation by L. Bottura (August 2004) MAC presentation by L. Bottura (December 2004) Options for a partial/staged implementation Option 1 (RHIC Paradigm) Static magnetic field model Option 2 (Tevatron Paradigm) Parametric magnetic field model Off-line reference magnet measurements Off-line correction of model predictions Option 3 (HERA+Tevatron Paradigms) Parametric magnetic field model On-line reference magnet measurements On-line correction of model predictions Reference Magnet System (RMS) conceptual design review

  17. Status as of November 2004 • Given the present priorities (production, testing, installation) it is not foreseen to realize a system as complex as the “option 3” of the proposed RMS • However, the test benches will be kept alive after end of the series tests for special measurements/re-measurements of magnets • Work on models and instrumentation proceeds aside main tasks (staffed by PJAS, DOCT, TECH) on: • model specification for MB’s, development for MQ’s • special tests on injection behavior • digital integrator for faster (3 Hz) magnetic measurements • fast (10 Hz), Hall-plate based sextupole measurements during snap-back On day-1 we will have a system with minimum capability (option 1 …) augmented by off-line measurements (… and 1/2)

  18. Some open issues • Make order in the data collected (3 databases used today) • homogenize (formats, units, reference frames) • centralize (database views) • secure data for > 15 years of operation • Define a common interface for beam tracking calculations as well as for LHC operation • the two tasks have similar requirements, but different time scales • work will foster discussion with users on needs and solutions • Provide validated models for the magnet behaviours • MB’s (on-going, to be completed) • MQ’s (little done so far) • other magnet types (to be done from scratch). A sample of specific issues: • hysteresis in the transfer function of correctors • field errors generated in correctors • operation of MQM at low field • IR magnets

  19. A starting point for the conceptual design of the LHC magnetic model

  20. Conclusions - 1/2 • Warm and cold measurements can be used integrally for the commissioning and initial operation of the LHC. No measurement goes in the trash bin. • Magnet setting and correction forecast is a non-linear problem. Feasible, but requires today: • cross-calibration between measurements to decrease the error margins on settings (e.g. transfer function for quads and higher order correctors) • special measurements to have a sufficient sample for interpolation and extrapolation of field errors (e.g. b3 at injection and ramp) • studies to establish a physical description of field and errors to provide a robust model for control (e.g. corrector hysteresis) i.e. bench time and manpower

  21. Conclusions - 2/2 • There is a need to unify data, aiming at making practical forecast easily available to users (AB-ABP, AB-OP) • start activity aiming at a LHC magnetic model for tracking studies (first priority) and LHC control (later) • The work on instrumentation is pursued as basic technology development within the core activity of the AT department. The schedule is not necessarily tied to LHC start-up • initial measurements, on demand of LHC-OP, may be done with the series test system, at reduced rate, and will require considerable processing (weeks) to perform re-calibration of the machine model • the off-line measurement system presently designed will not be suitable for on-line operation in real-time (the scope of the development has been limited). On-linereference magnets, as in HERA, are ruled out for the commissioning of LHC

  22. Appendix - The field model • Field and field errors are assumed to have different origins (components) that have clearly identified physical origin (e.g. geometric, persistent, saturation, …) • General functions for each component are obtained fitting cold data as a function of current or time, using functional dependencies that are “epexcted” from theory, or “practical” in describing data • Scaling parameters are applied to the general functions to model single magnets • The scaling parameters are either • measured (injection, mid-field, flat-top), or • extrapolated from warm conditions (geometric), or • extrapolated from averages measured (persistent currents for the same cable combination). • The field and field errors are obtained from the linear superposition of all components

  23. Geometric multipoles • important at all field levels • absolute field is linear in current, normalised field is constant • measured in warm conditions (can be extrapolated from industry data)

  24. Persistent currents • mostly important at low field (but present throughout) • proportional to the magnetization M • proportional to Jc • assume that the Jc(B) scaling is maintained, geometry and B distribution effects are condensed in fitting exponents a and b aditional T-dependence of Jc to be added

  25. Iron saturation • important at high field only • associated with details of iron geometry (shape of inner contour, slits, holes, …) • no “theoretical” expression available, apart for the general shape of the saturation curve (sigmoid) that provides a convenient fit to experimental data

  26. Decay • appears during constant current excitation • associated with current redistribution in the superconducting cables • result of a complex interaction: current redistribution  local field  magnetization  bore field • assume that the dynamics follows that of current diffusion

  27. Powering history effects • average effect of powering history has an uncertainty due to limited sampling (2 % of production ?) 3 magnets 2 magnets

  28. I tFT tpreparation IFT tinjection t Powering history dependence • main parameters: • flat-top current • flat-top duration • preparation time before injection • (injection duration)

  29. Snap-back • first few tens of mT in the acceleration ramp, after injection • pendant to decay: magnetization changes are swept away by background field • result of a complex interaction: current ramp  background field  magnetization  bore field • Db1 and Dcn obtained from the decay scaling at end of injection • DI obtained from magnet family invariant (found by serendipity)

  30. Look at the data the right way… exponential fit fit of the b3 hysteresis baseline hysteresis baseline subtracted b3 snap-back singled out

  31. … and they correlate ! Same magnet, different cycles Db3andDI change for different cycles…

  32. An invariant for snap-back !?! the correlation plot holds for many magnets of the same family

  33. Magnetic Reference System (RMS) conceptual design

  34. RMS options • Option 1 (RHIC Paradigm) • Static magnetic field model • Option 2 (Tevatron Paradigm) • Parametric magnetic field model • Off-line reference magnet measurements • Off-line correction of model predictions • Option 3 (HERA+Tevatron Paradigms) • Parametric magnetic field model • On-line reference magnet measurements • On-line correction of model predictions

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