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SCU Next Phase Meeting

SCU Next Phase Meeting. July 8, 2014. Point # 1. Joining of two 1.5 m undulators. Two undulator with individual end terminations (in close proximity to one another) Need a phase shifter due to drift space Need precise alignment of the two undulators to one another

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SCU Next Phase Meeting

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  1. SCU Next Phase Meeting July 8, 2014

  2. Point # 1 Joining of two 1.5 m undulators • Two undulator with individual end terminations (in close proximity to one another) • Need a phase shifter due to drift space • Need precise alignment of the two undulators to one another • Can be tuned independently • Joining of two undulator cores with no end terminations in the junction between the two halves • Requires precise alignment of two halves (magnetic interface) • No need for a phase shifter • Essentially forming one undulator with the two cores • Requires measurements and tuning on the full 3 m length

  3. Point # 1 Phase Mismatch • Contributions to the phase shift from the drift section and the end fields Slippage from break section: Phase vs main current for different Lb: Length of break section Phase error due to break: Phase integral required for 2π correction:

  4. Point # 1 Conceptual Phase Shifter Layout • Compact phase shifter uses one end corrector from each undulator and one extra dipole magnet in between • Distance between the undulator cores ~ 13 cm for this layout (could be reduced if alignment quadrupoles are not necessary) • Joint sections for Nb3Sn undulator are 4 cm long for each core Alignment Verification Quadrupoles / Bx correction Second Field Integral with phase shifter -2k Lb +k +k Lb Phase shifter dipole End corrector End corrector

  5. Point # 2 Quadrupole Concept • Conceptual design of a compact quadropole • Directly attached to the undulator cold mass • Integrated quadrupole strength of 4 T (LCLS-II quad strength) can be obtained • Independently powered coils can be used for x-field correction Quadrupole Magnet End corrector

  6. Point # 4 Vertical Alignment with Alignment Quadrupoles • Use reference quadrupoles at each end of the 3 m structure • Tuning and calibration is based on the line between the magnetic center of the two quadrupoles • Fiducialization can be performed with a wire measurement and referenced to fiducials on the outside of the cryostat • Allows for beam based alignment by moving the cryostat to find the center of the quads with the electron beam Full Length Quadrupole Small Alignment Quadrupole

  7. Point # 4 Vertical Alignment with Magnetic Center • Pulsed wire can be used to find the magnetic center with high precision by measurement of natural focusing of the undulator • Coupling between axial field and wire deflection leads to a vertical force on the wire when the wire is placed off-axis • Null measurement (zero signal when wire is centered with the undulator) Measurement of Dynamic Effects on ALS EPU Dynamic effects are due to the coupling between axial field and field gradients with the undulating wire

  8. Point # 4 External Fiducialization • Pulsed can be placed in the center of the undulator or quads • Wire detectors can be fiducialized and used to find the two ends of the wire • Wire position can be related to external fiducials on the cryostat based on the cold magnetic measurements Pulsed Wire Fiducialization Fiducialized Detector can be used to find wire location Wire inside vacuum chamber A second detector will be added to find both ends of the wire

  9. Point # 5 Horizontal Field Correction • End correction can be performed using independent coils on the quadrupole correctors • From experience with LCLS-II PM Hybrid undulators it is expected that end correctors should be sufficient • Local x-field errors are small but can lead to random-walk drift • For SCUs it is expected that x-field errors will be small LCLS-II PM Hybrid Undulator Experience Second Integral after Tuning Second Integral after Dipole Correction LCLS-II Requirement

  10. Point # 5 Phase Errors Including x-Field • Phase error was calculated with and without the x-field contribution • The contribution of the x-field errors to the overall phase error is small for the errors that were encountered in the LCLS-II one meter hybrid undulator prototype • Expect similar result from SCUs where local x-field errors should be small Phase Error at Minimum Gap (7.2 mm) Phase Error at Maximum Gap (20 mm)

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