Uncertainty on magnetic measurements of the LHC magnets

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Uncertainty on magnetic measurements of the LHC magnets at CERN M. Gateau, L. Bottura,

Uncertainty on magnetic measurements of the LHC magnets at CERN M. Gateau, L. Bottura, M. Buzio, S. Sanfilippo M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 1 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 2 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 3 / 19

The 3 magnetic measurement systems used for cold characterization of LHC magnets (1) ØField

The 3 magnetic measurement systems used for cold characterization of LHC magnets (1) ØField quality needs to be determined with high accuracy Ø 10 -20% of the 1706 cryo-assemblies will be measured magnetically during cold series tests Ø 3 systems for magnetic measurements at cold 1) • • 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 A pair of shafts for measurements of 15 -meterlong dipoles M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch Superconducting dipole on the cold test bench in SM 18 equipped with rotating coil system 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 4 / 19

The 3 magnetic measurement systems used for cold characterization of LHC magnets (2) 2)

The 3 magnetic measurement systems used for cold characterization of LHC magnets (2) 2) Automated scanner Used for SSS & special SSS’s of variable lengths One 600 mm-long rotating coil Longitudinal scanning over magnet length Voltage integral vs. angular position Integrated gradient & local multipoles of quadrupoles, (axis) • • • 3) Single Stretched Wire (SSW) Installation of SSW for special SSS measurement Automated scanner installed on the special SSS’s test bench in SM 18 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) • M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 5 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 6 / 19

Uncertainty on magnetic field Measurement uncertainty = random error + systematic error To fulfil

Uncertainty on magnetic field Measurement uncertainty = random error + systematic error To fulfil requirements of the beam dynamics, the main field should be known: n better than 8 n units of uncertainty for dipoles better than 10 units of uncertainty for quadrupoles From cold measurements, we expect to reach n less than 1 unit on main field random error for dipoles & quadrupole n 0. 1 units or better on higher harmonics random error n few units on systematic error M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 7 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 8 / 19

Rotating coils - Recent results on dipole field integral b 1, (bn & an)

Rotating coils - Recent results on dipole field integral b 1, (bn & an) normalised multipoles (n = 2 to 15) (bn&an) <0. 02 units (units) (b 1)<1 unit MB 3348 - Measurement repeatability on integrated field @ 11850 A n. Shafts are not identical: in this particular case, the rotating coil of aperture 1 gives higher accuracy for multipoles n. Zero sensitivity for n = 12. 5 due to measurement coil geometry WITHIN EXPECTED LIMITS M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 9 / 19

per bn&an (units) Rotating coils - Noise study Magnet current (A) MB 1222

per bn&an (units) Rotating coils - Noise study Magnet current (A) MB 1222 - Noise analysis on normalised multipoles vs. current n. Noise signal is decreasing as magnet current is increasing ELECTRICAL NOISE n. At high currents, noise signal is constant NOISE MECHANICAL COMPONENT Current ripple not compensated on b 1 M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 10 / 19

Rotating coils - Noise on integrator input |∆ n|=N. L. 2 sin(n /2). rn/rrefn-1.

Rotating coils - Noise on integrator input |∆ n|=N. L. 2 sin(n /2). rn/rrefn-1. . T. |∆Cn|/(n-1). G with integration period T = 7 ms per flux n (V. s) Magnet current (A) MB 1222 - Noise analysis on flux n. Noise on flux is of the order of noise limit of VFC (Voltage to Frequency Converter) integrators we use n. For higher frequency integration, R&D with A/D converters has started (see talk of A. Masi, Fast devices, Tuesday) M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 11 / 19

Rotating coils - No degradation with time In year 2000 On b 1 (units)

Rotating coils - No degradation with time In year 2000 On b 1 (units) On higher orders Current (A) Bench Other info MB 3348 0. 57 10 e-3 11850 F 2 With PGAs MBP 201 0. 14 > 10 e-3 5000 A 2 Without PGAs MB 1017 0. 13 NA 5000 A 2 With PGAs MB 1022 0. 27 10 e-3 5000 F 2 With PGAs Factor affecting repeatability: q q q Standard deviation averaged on 12 sectors of different magnets Noise on current Mechanical noise (rotation) Electrical noise (cabling of bench) Integrators offset adjustment Measurement environment (temperature, humidity) STILL WITHIN EXPECTED TOLERANCES M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 12 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 13 / 19

B 1 (T) Rotating coils - Same magnet measured with 2 different coils (1)

B 1 (T) Rotating coils - Same magnet measured with 2 different coils (1) Position of the 12 measurement coil center on magnet length (mm) MB 1222 - Main field @ 11850 A measured with 2 different coils n. Confirmation of reliable and stable coil calibration (see talk of O. Dunkel, Coils, Tuesday) n. Average systematic error on B 1 between the 2 measurements = 2. 34 units M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 14 / 19

Rotating coils - Same magnet measured with 2 different coils (2) Difference between the

Rotating coils - Same magnet measured with 2 different coils (2) Difference between the 2 positions (units) b 1≈2. 34 units bn&an<0. 2 units b 1, (bn & an) normalised multipoles per sector (n = 2 to 15) MB 1222 - Field difference @ 11850 A measured with 2 different coils n. Cross-check on rotating coils system gives very conclusive results WITHIN TOLERANCES M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 15 / 19

Difference between the 2 systems on b 1 (units) SSW & rotating coils -

Difference between the 2 systems on b 1 (units) SSW & rotating coils - result comparison Magnet & magnet aperture Field difference on B 1 @ 11850 A measured with 2 different systems n. Comparison between SSW & rotating coils gives a difference of 5. 5 units at maximum (1. 98 units in average) n. The difference between the 2 systems is within expectations WITHIN TOLERANCES M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 16 / 19

SSW & automated scanner - result comparison Cold TF (T/k. A) Warm data: Courtesy

SSW & automated scanner - result comparison Cold TF (T/k. A) Warm data: Courtesy of P. Hagen & E. Todesco, CERN 17 units Warm mole TF (T/k. A) W/C correlation of the field gradient transfer function using 2 systems of measurements at cold n. 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) M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 17 / 19

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility

Overview n Introduction n Uncertainty on magnetic field n Repeatability of measurements n Reproducibility of measurements n Summary & Conclusion M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 18 / 19

Uncertainty (units @ 17 mm) Summary & Conclusion 8 units on B 1 10

Uncertainty (units @ 17 mm) Summary & Conclusion 8 units on B 1 10 units on B 2 Courtesy of L. Bottura, CERN Uncertainty on the 3 systems n. Uncertainty on the dipole main field is of the order of 3 to 5 units for all systems used and sufficient for LHC requirements n. 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 M. Gateau CERN – Geneva – CH maryline. gateau@cern. ch 14 th International Magnetic Measurement Workshop 26 -29 September 2005, Geneva, Switzerland 19 / 19