SCU Next Phase Meeting
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Transcript of SCU Next Phase Meeting
SCU Next Phase Meeting
July 8, 2014
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
Point # 1
Phase Mismatch• Contributions to the phase shift from the drift section and the
end fields
Slippage from break section:
Phase error due to break:
Phase integral required for 2π correction:
Length of break section
Point # 1
Phase vs main current for different Lb:
200 400 600 800 1000 1200 1400 16000
200
400
600
800
1000
1200
1400
1600
1800
406080
Je (A/mm2)
Phas
e sh
ift (⁰
)
Lb
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
End corrector End correctorPhase shifter dipole
Alignment Verification Quadrupoles / Bx correction Second Field Integral
with phase shifter
Point # 1
Lb
+k +k
-2k
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
End correctorQuadrupole Magnet
Point # 2
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
Small Alignment Quadrupole
Full Length Quadrupole
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
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
Wire inside vacuum chamber
Fiducialized Detector can be used to find wire location
A second detector will be added to find both ends of the wire
Point # 4
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
Point # 5
Second Integral after Dipole CorrectionSecond Integral after TuningLCLS-II PM Hybrid Undulator Experience
LCLS-II Requirement
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)
Point # 5