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Support System and Alignment

Support System and Alignment. Sushil Sharma ME Group Leader ASAC Review of NSLS-II July 17-18, 2008. Support System and Alignment Team.

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Support System and Alignment

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  1. Support System and Alignment Sushil Sharma ME Group Leader ASAC Review of NSLS-II July 17-18, 2008

  2. Support System and Alignment Team R. Alforque, M. Anerella, C. Channing, L. Doom, G. Ganetis, P. He, A. Jain, P. Joshi,P. Kovach, F. Lincoln, S. Plate, V. Ravindranath, J. Skaritka and Alexander Temnykh(Cornell University, Ithaca, NY)

  3. Outline • Introduction • Alignment specifications • Support design concept • Magnet alignment and positioning • Girder alignment and positioning • Stability specifications • Vibration – FE analyses and measurements • Thermal – FE analyses and test setup • Conclusions

  4. Introduction LOB Booster Storage Ring Storage Ring Cell • Energy: 3 GeV • Circumference: 792 m • Lattice: 30 DBA Cells (15 Super periods) • Low Emittance: 2 nm-rad without damping wigglers • 0.6 nm-rad with damping wigglers (56 m) The low-emittance lattice has stringent alignment and stability requirements that have been met by innovative and cost-effective solutions.

  5. Design Requirements – SR Support System Alignment For acceptable dynamic aperture the SR support system must meet the following alignment requirements: * 30 µm is the goal; acceptable limit is 50 µm. An analysis of tolerance stack-up shows that 30-50 µm alignment is not possible with conventional support designs and alignment techniques.

  6. Girder Support Design Corrector Magnet Sextupole Magnet Quadrupole Magnet Vacuum Chamber Girder Floor Plate Dispersion Girder: Weight - 3200 kg Length - 4.83 m Width - 0.86 m Height - 0.55 m • The design was developed incorporating alignment and stability requirements. • Beam height of 1.2 m. • The design is cost-effective – conventional fabrication. • 8 point support system to raise resonant frequencies. • The girder and the magnets are aligned by removable alignment mechanisms. • After alignment the components are locked in place by stiff bolts.

  7. Vibrating Wire Alignment Technique - R&D Wire Vibration detectors (LED phototransistors, ~ 13 mV/micron) X-Y Stages • A tensioned wire is stretched through the bore of the magnets. The wire is mounted on high-precision X-Y translation stages. • An AC current is passed through the wire. The AC frequency is chosen to generate a resonant anti-node at the magnet to be aligned. • Any transverse magnetic field excites the resonant mode of the wire. • The vibration amplitude is measured with LED detectors . The wire is displaced in both x-y directions to obtain a minimum vibration amplitude. • Magnet movers are then used to position the magnet on the nominal wire axis. • The wire sag can be determined to within 1 from its first resonant frequency. The vertical position of the magnet is adjusted for this sag. Granite table for supporting magnets during R&D phase Magnet movers(1 micron resolution)

  8. Vibrating Wire Alignment Technique (contd.) Magnet Movers • Software is being developed to automate the entire alignment process. In the final step, the magnets are fastened to the girder by manually applying torques to the 4 sets of nuts. • Tests have shown that the magnets can be fastened to the desired positions to within 5 µm in 3-5 minutes. Magnet Torque Test

  9. Quadrupole Measurements: Horizontal Scans 14-Jan-2008 X Center is given by intersection with 0A line The magnet center can be located to within 4 μm.

  10. Sextupole Measurements: Horizontal Scan Parabolic fits Horizontal center, defined as the point of zero slope in B_y Vs. X, can be located to within 5 μm.

  11. Girder Positioning and Alignment • Removable girder positioning fixtures are placed under each end of the girder. • Horizontal position adjustment is made by differential screws , vertical by open-end wrenches. • 90% to 95% of girder weight is supported by flexible air jack to minimize loads on adjustment assembly • All girder positioning is accomplished to within 50 μm with a laser tracker. X-Y positioning fixture Laser tracker Integral air jack Differential screws provide .002mm per degree of hand wheel rotation Girder with positioning fixtures installed

  12. Recovery of Girder Profile Upper fiducial Lower fiducial • The girder deflection under the combined weights is ~ 140 µm. • The “elastic” deflection has a scatter of ~ 15 µm. • Laser trackers can be used to recover the girder profile to within ~ 15 µm. • Digital inclinometers are being considered to recover the profile to within ~ 5 µm. Right indicator Left indicator

  13. Tightening Torque • Resonant frequency tests showed that it is necessary to torque the bolts to ~1000 lb-ft. Torque wrench with 13:1 torque multiplier Hydraulic torque wrench with split head design

  14. Stability Requirements Stability Requirements (Vibration and Thermal) • Up to 4 Hz the motions of the magnets-girder assemblies are assumed to be correlated (the wavelength of shear waves at 4 Hz is ~ 70 m, as compared to the 26.4 m length of a DBA cell). • The global orbit feedback system is expected to correct the motion in this low frequency range.

  15. Ambient Ground Motion RMS Displacements at CFN (N. Simos) ( 0.5 - 4) Hz : 145 nm (4 - 30) Hz : 14 nm (30 - 100) Hz : 1 nm Support System Design Approach: First resonant frequency > 30 Hz  the rms motion that will be amplified by the magnets-girder assembly is only 1 nm.

  16. Girder Vibration Tests Constrained Girder Girder with Dummy Weights Vibration tests were performed on: • Unconstrained girder • Constrained girder • Constrained girder with dummy weights

  17. Modal Analysis – Unconstrained Girder Rocking Mode, 42 Hz Bending Mode, 58 Hz Twisting Mode, 112 Hz • Impact testing: Horizontal impulse excitation provided by a soft-tipped hammer. • Peaks in the PSD curve –natural frequencies • Good agreement between FEA and experiment

  18. FEA Model Calibration Young’s modulus of the 2” bolt reduced by a factor of 10 • With the modification, the modal analysis results agree better with the measured natural frequency of the girder at 1000 ft-lbs • FEA Rocking mode = 86 Hz (Measured  85 Hz) • FEA Twisting mode = 110 Hz (Measured  120 Hz) Rocking Mode Twisting Mode

  19. Vibration Tests on the Girder with Weights MODE 1 ~40 Hz • Modal analysis of the adjusted girder model with 5000 lbs weight • FEA Rocking mode:45 Hz (Measured  40 Hz) • FEA Twisting mode:56 Hz (Measured  60 Hz)

  20. Modal Analysis - Girder- Magnet Assembly • The calibrated model was used to estimate the natural frequencies of the final girder-magnet system • Rocking mode = 34 HZ • Twisting mode = 51 HZ • Vibration tests will be performed with prototype magnets. • Modeling of the interface between the girder, bolts and base plates will be refined.

  21. Thermal Stability of the Girder Support System Maximum vertical misalignment between the magnets: ~0.014 μm (tolerance = 0.025 μm ) Maximum vertical deflection of the vacuum chamber at the BPM locations (near Invar supports) : ~ 0.14 μm (tolerance = 0.20 μm)

  22. Thermal Stability Tests DVRT (Displacement Variable Reluctance Transducer) • A thermally stable (± 0.1 ºC) enclosure has been built. • Displacement sensors (DVRTs) of 15 nm resolution have been procured and tested.

  23. User-BPM Support Stands User-BPM Supports BPM Assembly Composite Support Stand Mechanical stability requirement: ±0.1 μm (rms, 4-50 Hz) • Four 10-inch diameter carbon-fiber composite support stand are in procurement. • Thermal expansion coefficient :< 0.1 μm/m/ºC. • The BPM assembly is supported at its mid-plane. • First natural frequency = ~ 100 Hz

  24. Conclusions • FE analyses, alignment tests and vibration measurements show that the prototype designs can meet the alignment and stability requirements. • Vibrating wire alignment tests have proven that the multipole magnets can be aligned to within 5 μm. • Girder alignment and positioning tests are ongoing. Initial results show that the girder can be positioned to within 50 μm with a profile repeatability of 15 μm. • With a calibrated FE model the lowest resonant frequency of the girder-magnet assembly is estimated to be ~ 34 Hz. This ensures that there is essentially no magnification of the ground motion by the girder-magnet assembly. • A temperature-controlled enclosure has been built for thermal stability tests on the girder and user-BPM support systems. Acknowledgment: Stability – L-H Hua, S. Kramer, S. Krinsky, I. Pinayev, O. Singh, F. Willeke Design – T. Dilgen, B. Mullany, D. Sullivan, W. Wilds

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