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SNS Magnet Measurements at ORNL

14th International Magnet Measurement Workshop, CERN, Sept. 26-29. SNS Magnet Measurements at ORNL. J. G. Wang SNS, ORNL. Acknowledgements: Ted Hunter (Team Leader), Doug LeBon, Robert McBrien, Steven Heimsoth. SNS Facility. Tasks of SNS Magnet Measurements at ORNL.

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SNS Magnet Measurements at ORNL

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  1. 14th International Magnet Measurement Workshop, CERN, Sept. 26-29 SNS Magnet Measurements at ORNL J. G. Wang SNS, ORNL Acknowledgements: Ted Hunter (Team Leader), Doug LeBon, Robert McBrien, Steven Heimsoth

  2. SNS Facility

  3. Tasks of SNS Magnet Measurements at ORNL • 281 Magnets for SNS Linac:In operation 164 Magnets (EMD & PMQ) for DTL 51 Quads for CCL 66 8Q35 Quads for SCL • 70 Magnets for SNS HEBT:Installed 9 8D533 Dipoles 1 8D406 Dipole 33 12Q45 Quads 8 21Q40 Quads 15 16CD20 Dipole Correctors 4 27CD30 Dipole Correctors • 45 Magnets for SNS RTBT:In installation 15 27CD30 Dipole Correctors 24 21Q40 Quads 2 30Q58 Quads 2 30Q44 Quads 1 17D244 Dipole: (to be measured) 1 41CDM30 corrector for Ring Injection dump

  4. Criteria for SNS Linac and Transfer Line Magnet Tests • Integrated field (B*L) for dipoles and integrated gradient (G*L) for quads are measured, and the Integrated Transfer Functions (ITF) are obtained. • B*L non-uniformity in a dipole should be less than 1/1000. • ITF spread in a chain of magnets powered by the same supply should be less than 1/1000. • Integrated harmonic amplitude should be less than 50 units (1 unit = 0.01% of main integrated field/gradient). • Field repeatability after re-assembly should be less than 0.02%. • Magnetic center is less than 10 mm from the search coil center, with respect to which the magnet is fiducialized. • Cycling current, cooling water flow rate/pressure, and inlet/outlet temperatures are recorded.

  5. Magnet Measurement Systems @ ORNL Four test stands developed to handle magnets as small as DTL PMQ and as large as any size. Two different kinds of search coils to detect magnetic flux: One translational coil for HEBT dipoles 8D533 and 8D406. Seven rotational coils of the Halbach type for all other magnets Three electronic systems including digital integrator, digital tesla meter, digital voltage meter, power supplies, current sensors, etc. Labview software for test control and on-line data processing.

  6. SCL 8Q35 Quads Measurements (1) • SCL employs 9 singlets and 28 doublets of 8Q35 quads. • A rotational coil of the Halbach type was employed to measure the excitation curves, harmonic contents, and steering power. • The ITF curves spread rather widely and have different slopes for many quads.

  7. SCL 8Q35 Quads Measurements (2) • 66 8Q35 quads have large spread in ITF; At 350 A, <ITF>=5.887E-3 T/A with StDev=0.15%. • ITF spread is mainly due to mechanical aperture errors, as evidenced by the correlation between <ITF> and 1/R2. • The rather different slopes of ITF curves of many quads are not understood yet. • The magnets tested as received are sorted and paired to guarantee the doublet ITF within 0.1%.

  8. SCL 8Q35 Quads Measurements (3) • The dominant harmonic term is dodecapole, which has amplitude of about 30 units (Rref=3 cm).  • At 350 A, <C6>=29.75 units with StDev=5.3%; and <C10>=7.75 units with StDev=7.3%. • Un-allowed terms, C3,C4,C5, are more randomly distributed, indicating mechanical errors in manufacture.

  9. HEBT/RTBT 21Q40 Quad Measurements • 8 tested at 300-460 A for HEBT: <ITF>= 3.1155E-3 T/m with StDev=0.024% at 360 A. • 24 tested at 300-1000 A for RTBT: <ITF>= 3.1054E-3 T/m with StDev=0.031% at 750 A. • The magnet are sorted to guarantee ITF within 0.1% for same power chain.

  10. 21Q40 Quad Harmonics • The harmonics are evaluated in a reference radius of 8 cm; • Dodecapole changes with current, indicating iron saturation; • Sextupole is often larger due to mechanical errors; • Overall, all harmonics are small enough for HEBT & RTBT.

  11. HEBT Dipole 8D533 Measurements • A translational coil (6.3 m long & 1 cm wide) was employed. • B*L non-uniformity across the gap is less than 1/1000 for 1 GeV operation. • <B*L>of 7 dipoles on a common supply, is 1.11 T-m with StDev of 0.049% for 1 GeV operation.

  12. RTBT Dipole 17D244 to be Mapped A H-shaped dipole with curved pole tips; Weigh 46000 LB; A rotating search coil of 3.8 m long with support at two ends & middle point has been developed to map the dipole in the RTBT tunnel. The B*L along a curved beam trajectory has to be reconstructed based on test results.

  13. RTBT Dipole 17D244 Simulations • A straight, rotating patch yields B*L=1.5773 T-m and harmonics as shown in plot. • Integration over a curved beam trajectory yields B*L=1.5837 T-m

  14. Test Parameters

  15. Summary • There are 396 magnets (including a few spares) for the SNS linac and transfer lines, measured at ORNL (additional 20 PMQ’s were tested and found failed). • They all meet specifications by sorting or pairing based on the test results! The magnets for SNS linac are already in operation. Only one RTBT dipole 17D244 is waiting for tests. • Accurate magnet measurements will play important role in SNS commissioning, operation, and upgrade. • The SNS magnet team will move forward to design, develop and measure the magnets for SNS upgrade.

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