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Overview

Uncertainty on magnetic measurements of the LHC magnets at CERN M. Gateau , L. Bottura, M.Buzio, S. Sanfilippo. Overview. Introduction Uncertainty on magnetic field Repeatability of measurements Reproducibility of measurements Summary & Conclusion. Overview. Introduction

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Overview

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  1. Uncertainty on magnetic measurements of the LHC magnets at CERNM. Gateau, L. Bottura, M.Buzio, S. Sanfilippo 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  2. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  3. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  4. The 3 magnetic measurement systemsused for cold characterization of LHC magnets (1) • Field quality needs to be determined with high accuracy • 10-20% of the 1706 cryo-assemblies will be measured magnetically during cold series tests • 3 systems for magnetic measurements at cold • Rotating coils • Used for dipoles or Short Straight Sections (SSS) of standard length • 12 sectors for dipoles & 6 for SSS’s over total magnet length • Voltage integral vs. angular position is recorded • Field strength & multipoles for dipoles, quadrupoles and associated correctors Superconducting dipole on the cold test bench in SM18 equipped with rotating coil system A pair of shafts for measurements of 15-meter-long dipoles 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  5. The 3 magnetic measurement systemsused for cold characterization of LHC magnets (2) • Automated scanner • Used for SSS & special SSS’s of variable lengths • One 600mm-long rotating coil • Longitudinal scanning over magnet length • Voltage integral vs. angular position • Integrated gradient & local multipoles of quadrupoles, (axis) Installation of SSW for special SSS measurement Automated scanner installed on the special SSS’s test bench in SM18 • Single Stretched Wire (SSW) • Can be used on any length of magnet • 1 wire loop over total magnet length • Voltage integral vs. wire displacement in transversal plane • Integrated strength of quadrupoles and dipoles,(field direction, magnetic axis) • (See talk of G. Deferne, Fiducialisation/ Alignment / Axis, Today) 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  6. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  7. Uncertainty on magnetic field To fulfil requirements of the beam dynamics, the main field should be known: • better than 8 units of uncertainty for dipoles • better than 10 units of uncertainty for quadrupoles From cold measurements, we expect to reach • less than 1 unit on main field random error for dipoles & quadrupole • 0.1 units or better on higher harmonics random error • few units on systematic error Measurement uncertainty = random error + systematic error 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  8. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  9. Rotating coils - Recent results on dipole field integral b1, (bn & an) normalised multipoles (n = 2 to 15) (b1)<1 unit  (units) (bn&an)<0.02 units MB3348 - Measurement repeatability on integrated field @ 11850A • Shafts are not identical: in this particular case, the rotating coil of aperture 1 gives higher accuracy for multipoles • Zero sensitivity for n = 12.5 due to measurement coil geometry • WITHIN EXPECTED LIMITS 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  10. Rotating coils - Noise study  per bn&an (units) Magnet current (A) MB1222 - Noise analysis on normalised multipoles vs. current • Noise signal is decreasing as magnet current is increasing ELECTRICAL NOISE • At high currents, noise signal is constant NOISE MECHANICAL COMPONENT Current ripple not compensated on b1 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  11. Rotating coils - Noise on integrator input |∆n|=N.L.2sin(n/2).rn/rrefn-1..T.|∆Cn|/(n-1).G with integration period T = 7 ms Magnet current (A)  per flux n (V.s) MB1222 - Noise analysis on flux • Noise on flux is of the order of noise limit of VFC (Voltage to Frequency Converter) integrators we use • For higher frequency integration, R&D with A/D converters has started(see talk of A. Masi, Fast devices, Tuesday) 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  12. Rotating coils - No degradation with time In year 2000 Standard deviation averaged on 12 sectors of different magnets Factor affecting repeatability: • Noise on current • Mechanical noise (rotation) • Electrical noise (cabling of bench) • Integrators offset adjustment • Measurement environment (temperature, humidity) STILL WITHIN EXPECTED TOLERANCES 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  13. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  14. Rotating coils - Same magnet measured with 2 different coils (1) B1 (T) Position of the 12 measurement coil center on magnet length (mm) MB1222 - Main field @ 11850A measured with 2 different coils • Confirmation of reliable and stable coil calibration(see talk of O. Dunkel, Coils, Tuesday) • Average systematic error on B1 between the 2 measurements = 2.34 units 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  15. Rotating coils - Same magnet measured with 2 different coils (2) b1≈2.34 units bn&an<0.2 units b1, (bn & an) normalised multipoles per sector (n = 2 to 15) Difference between the 2 positions (units) MB1222 - Field difference @ 11850A measured with 2 different coils • Cross-check on rotating coils system gives very conclusive results • WITHIN TOLERANCES 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  16. SSW & rotating coils - result comparison Difference between the 2 systems on b1 (units) Magnet & magnet aperture Field difference on B1 @ 11850A measured with 2 different systems • Comparison between SSW & rotating coils gives a difference of 5.5 units at maximum (1.98 units in average) • The difference between the 2 systems is within expectations • WITHIN TOLERANCES 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  17. SSW & automated scanner - result comparison Warm data: Courtesy of P.Hagen & E.Todesco, CERN Cold TF (T/kA) 17 units Warm mole TF (T/kA) W/C correlation of the field gradient transfer function using 2 systems of measurements at cold • The 17 unit offset correlate with the calibration uncertainty of 15 m on rotation radius (coil radial position should be known better than 8 m) 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  18. Overview • Introduction • Uncertainty on magnetic field • Repeatability of measurements • Reproducibility of measurements • Summary & Conclusion 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

  19. Summary & Conclusion Courtesy of L. Bottura, CERN 10 units on B2 Uncertainty(units @ 17mm) 8 units on B1 Uncertainty on the 3 systems • Uncertainty on the dipole main field is of the order of 3 to 5 units for all systems used and sufficient for LHC requirements • Uncertainty on the quadrupole main gradient of 5 (SSW) to 35 units (coils) has a large variability from system to system:SSW is at present our reference system 14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland

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