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