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Measurement of the first LINAC4 series PMQs

Measurement of the first LINAC4 series PMQs. R. Beltron Mercadillo, M . Buzio, D . Cote, G. Golluccio , O. Dunkel, L . Gaborit , D.Giloteaux , P . Galbraith, F. Mateo, L . Walckiers. Contents: Measurement instruments and method Summary of series test results Additional test results

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Measurement of the first LINAC4 series PMQs

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  1. Measurement of the first LINAC4 series PMQs R. Beltron Mercadillo, M. Buzio, D. Cote, G. Golluccio, O. Dunkel, L. Gaborit, D.Giloteaux, P. Galbraith, F. Mateo, L. Walckiers. Contents: Measurement instruments and method Summary of series test results Additional test results Conclusions and outlook

  2. Instrumentation and method

  3. Linac4 measurement bench • From September 2010 bench in I8 lab (ISR tunnel) • Better mechanical and thermal stability • Temporary magnet storage space (a cupboard)

  4. turn around longitudinal axis flip aroundvertical axis Multiple measurement configurations main objectives: - link the fiducial references on the magnet to the test bench references - Estimate systematic offsets (X,Y,α) rectified pin rests

  5. y x Field direction measurement Y XXX B2 PIN 1 ψ α X ψField direction,  measured field phase αAngular offset between coil reference frame and magnet frame

  6. y y` x` Dz=Dx+iDy x y x • Measured harmonics contain information about the magnetic axis • Assuming small offsets and one dominant harmonic, the center can be obtained by feed-down: • The computed ∆z is relative to the coil rotation axis → it must be transferred mechanically to the magnet references. Magnetic Axis Measurement Y XXX M (x,y) PIN 1 O(x0 ,y0) X x,yMagnet axis (M) x0, y0offset between magnet frame and coil frame (O)

  7. PMQ reference system for harmonics, axis, field direction

  8. The beam enters into the screen. • the PINS are on the opposite face. • The By component grows for increasing x (normal quadrupole). • If a pin is inserted in PIN2 makes the quadrupole DEFOCUSING for a H-beam. Polarity Convention

  9. Bench uncertainties Estimation done on R1 reference PMQall values RMS 1 

  10. Stretched Wire for GdL calibration • Iterative XY centring of the wire until x=y =0 • Reproducibility for 45 mm length, 2 Tm/m magnet about ± 0.2 % • Measured GdL is used to calibrate the productradius × area of the rotating coil • But: the measurement is affected by the error induced by higher order harmonics …

  11. Uncertainty in GdL calibration with Single Stretched Wire • “doctored” Aster PMQ Ref2 used in 2010 as a mutual calibration reference (main worry at the time: get the sextupole right) • detailed error analysis shows that GdL errors may add up to 0.5~1.0 % Stretched Wire GdL measurement: 2×averages from 4× wire movements (stroke=) y -x x -y assuming: perfect initial centering and roll alignment order or magnitude of expected errors for =10 mm: mitigating measures adopted from now on:- new 45 mm reference PMQ 121  one order of magnitude smaller errors- shorter wire stroke =7.5 mm (S/N found still acceptable)- more frequent cross-checks SSW vs. rotating coil

  12. Summary of test results • 16 PMQs of batch 3 (SSW + rotating coil) • 4 PMQs of batch 4 (SSW + rotating coil)

  13. GdL (SSW)

  14. GdL AVERAGE: 0.88 % σ: 0.1 % -The integrated measured gradient is systematically 0.88 % lower than the specified values -the GdL measured by the coil after the latest calibration (reference = PMQ 121) agrees with the SSW within the uncertainties of the 2 systems (0.2 % SSW and 0.3 % Rotating coil @ 1) -There are no systematic discrepancies between rotating coil and SSW

  15. Field direction wrt Pin 1 Angular bench offset AVERAGE: -3.2 mrad σ: 0.1 mrad Field direction AVERAGE: 0.06 mrad σ: 1.5 mrad

  16. Pin2-Pin1 orthogonality AVERAGE: 1.05 mrad σ: 0.9 mrad

  17. Pin orthogonality vs. field direction no correlation

  18. Magnet Axis (M) Magnetic axis (mean ± ): X = 0.00 ± 0.03 mm Y = -0.01 ± 0.03 mm Bench offset (mean ± ): X0= -0.04 ± 0.01 mm Y0= -0.15 ± 0.00 mm

  19. Magnet Axis (M) Y X no correlation

  20. Harmonics @ 7.5 mm - CERN vs. Aster BEST MAGNET: 107 Cumulative multipole field error <= 1.0 %

  21. Harmonics @ 7.5 mm - CERN vs. Aster Cumulative multipole field error <= 1.7 % WORST MAGNET 113

  22. Harmonics @ 7.5 mm Error bar 2σ

  23. Additional test results

  24. Comparison Ti/Steel yokes

  25. Drift tube measurements • The test bench is equipped with a suitable support for DT measurements • Measurements done in 09/2010 on a DT prototype were affected by the rotating coil (19 mm) scratching the DT bore • A new coil with reduced 18.5 mm is expected in 05.2010

  26. High gradients and Elytt PMQ prototypes

  27. Vibrating Stretched Wire Systems • Vibrating wire system (FNAL system adapted at CERN): when AC current is passed through the wire, a Lorentz force is exerted by the magnetic field and excites a periodic oscillation . In the quad center no field, so no vibration. • Unique method for very small aperture magnets (CLIC) • Novel development: integrated harmonicsby stepwise scanning around a circular path • Preliminary results on 113 match very well harmonics obtained by rotating coil (however: tests on other magnets are not consistent) • Further development: longitudinal axis localization in an assembled DTL tank (TBC) XY long-range translation stages XY micrometric stages XY vibration amplitude = f() wire XY optical wire position detectors harmonic analysis Linac4 113 PMQ

  28. The GdL of the first 20 series PMQs is about 1% smaller than specified due to a calibration error • Absolute GdL can from now on be guaranteed within ≤0.3% uncertainty (including both manufacturing and measurement errors) • Significant allowed and non-allowed multipole errors are found up to n=6, all well within tolerance individually • About ½ of the PMQ exceed significantly the 1 mradfield direction tolerance • About ½ of the PMQ exceed significantly the 1 mradpin orthogonality tolerance Conclusions

  29. The remaining batch 4 PMQ shall be tested within the next few weeks • Upcoming 80 mm PMQs: a good quality unit must be set aside from the start as a calibration reference (Elytt prototype would be OK) • A new rotating coil should enable more accurate measurements (better B1, B2 bucking  immunity to mechanical errors) and prevent interference with DT • Documents in preparation: test reports updated with the most recent GdLcalibration + test method description • Raw/intermediate data to be made available in: dfs:\Departments\TE\Groups\MSC\MM\Linac4\L + final results in existing Oracle database Outlook

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