Undulator Development for SPring-8 XFEL

Takashi Tanakaon behalf of SPring-8 XFEL Insertion Device Group

Overview of SPringOverview of SPring--8 8 XFEL XFEL UndulatorsUndulators

XFEL at SPring-8

400m

250m

SPringSPring--88Storage RingStorage Ring

SPring-8 BL19LXU(1km Beamline)

Undulator Undulator BuildingBuilding

SCSS Test Acc.SCSS Test Acc.(EUV(EUV--FEL)FEL)

Accelerator Accelerator BuildingBuilding

Undulator Line@SP-8 XFEL

Drift Section• GV,PM,CT,BPM• Q. Magnet• Phase Shifter• Steering Magnet

磁石取付

磁石

磁石取付

磁石

H-Co r dierite8 0 0x700-V45

Q-D-V44ST-D-

V44

ST-D-

V44

磁石取付

磁石

磁石取付

磁石

Q-D-V44ST-D-

V44

ST-D-

V44

UN

D-ID

-1

磁石取付

磁石

5m1.15m

~110m

Undulator Segment

e- beam

FEL Radiation

SwitchingMagnet

Exp. Hutch

Undulator Line

ParametersElectron BeamElectron Energy 8 GeVBunch Charge 0.3 nCNormalized Emittance < 1πmm.mradSliced Energy Spread ~10-4

Repetition Rate < 60 HzUndulatorType In-Vacuum Planar

Period 18 mmMax. K @ Min. Gap 2.2 @ 3.5mmLength / Segment 5 mNumber of Segments 18

Magnet Circuit Hybrid, NdFeB

Peak Current 4 kABunch Length < 100 fsec

Note: all parameters are tentative

30 fsecPulse Length

FEL Radiation3.5x10-4FEL Parameter

~ 0.3 μradAngular Divergence (1σ)~ 1024Peak Flux~ 1033Peak Brilliance

~ 30 μmBeamsize (1σ)

~ 108Bose Degeneracy

30 GWSaturation Power75 mSaturation Length4.1 mGain Length

Undulator PrototypeUndulator prototype (2007)

Magnet inside the vacuum chamber

18mm

5m

R&Ds for XFEL Undulator

• We have several difficulties to be overcome if an IVU is chosen for the XFEL undulator:1. How to certificate the magnetic

performance of IVU after assembly?2. How to measure the real gap to

perform a precise control?

How to Certificate How to Certificate IVUIVU’’ssMagnetic Performance?Magnetic Performance?

Undulator Magnetic Measurement (1)

• Measurement of field distribution B(r)• Usually done with Hall-effect sensors• Necessary for field correction

– Optical phase error– Integrated multipole components

• Undulator field with shorter λu is more sensitive to r

Reliable system for Hall sensor actuation is necessary!

Undulator Magnetic Measurement (2)

long precise bench made of granite

Hall probe cantilever

magnet array

Conventional Measurement System

Hall sensor actuation with the massive bench made of granite○Low positional error×Free access required×Not portable

Undulator Magnetic Measurement(3)

•Measurement of IVUs– Conventional methods

cannot be applied!– Measurement w/o chamber– Installation of vacuum

chamber after checking the magnetic performance

Cross Section Cross Section of IVU Structureof IVU Structure

How is the magnetic reproducibility?

Magnetic Reproducibility in IVU?

Assembly

1. Detach the magnet array2. Install the vacuum chamber3. Reinstall the magnet array

How to Certificate the Performance?

•“In-situ” Measurement– We need to measure the magnetic

performance with both the vacuum chamber and magnet arrays installed.

• “In-situ” Correction– If the performance is found to degrade

during the assembling process, it should be corrected w/o removing the chamber.

In order to certificate the magnetic performances of IVUs,

InIn--situsitu Magnetic MeasurementMagnetic Measurement

In-situ Measurement with “SAFALI”

• Self-Aligned Field Analyzer with Laser Instrumentation– Simple system for Hall probe actuation

(not necessarily rigid or robust) – Monitor the Hall probe position with

laser beam and perform dynamic feedback

– Longitudinal position reading with a laser scale

SAFALI System for IVUTop View

Side View

undulator magnet

SAFALI System for IVUTop View

Side View

undulator magnet Hall probe

steppermotor

2-axis stagecarriagerail

SAFALI System for IVUTop View

Side View

undulator magnet Hall probe

steppermotor

2-axis stagecarriagerail

laser diode

PSDiris

SAFALI System for IVUTop View

Side View

undulator magnet Hall probe

steppermotor

2-axis stagecarriagerail

laser diode

PSDiris

corner cubelaser scale

InIn--situsitu Magnetic CorrectionMagnetic Correction

What can happen during assembly? (1)

• Mechanical frame is composed of 3 units

• Each unit is driven by 2 ball screws

Magnet gap of each unit can have a taper or offset

Gap OffsetGap Taper

Unit

Gap taper and gap offset due to unit structure

What can happen during assembly? (2)

Chamberassembly

Outer Beam

Inner Beam

Inner Supporting ShaftOuter Supporting Shaft

Deformation of the inner beam due to bad alignment of the supporting shafts

Vacuum Chamber

How to Correct the Induced Errors?

•Gap offset and taper– Perform fine gap tuning of each unit with

monitoring the magnetic field•Deformation of the inner beam

– Utilize “differential adjusters” as outer supporting shaft to correct the gap variation along the undulator axis.

Correction with Differential Adjuster

“Differential Adjuster” takes advantage of differential screw mechanism to adjust the total length. The structure is similar to a turnbuckle.

M30P1.2

M30P1.0

L

L can be adjusted by 0.2mm/rev.

Key Issues

turnbuckle

Example (1): Gap Fine Tuning

3.3o

0 200 400 600

-25

-20

-15

-10

-5

0

5

10

15

Phas

e Er

ror (

degr

ee)

Pole Number

0 200 400 600

-25

-20

-15

-10

-5

0

5

10

15

0 200 400 600

Phas

e Er

ror (

degr

ee)

Pole Number Pole Number

3.3o 7.2o

Example (1): Gap Fine Tuning

Assembling

0 200 400 600

-25

-20

-15

-10

-5

0

5

10

15

0 200 400 600

Phas

e Er

ror (

degr

ee)

Pole Number Pole Number

3.3o 7.2o

Example (1): Gap Fine Tuning

Assembling

1st 2nd 3rd

0 200 400 600

-25

-20

-15

-10

-5

0

5

10

15

0 200 400 600 0 200 400 600

Phas

e Er

ror (

degr

ee)

Pole Number Pole Number

Pole Number

3.3o 7.2o 3.3o

Example (1): Gap Fine Tuning

Assembling Fine Tuning

Example (2): Differential Adjuster

0 50 100 150 200 250

-15

-10

-5

0

5

10

15

0 50 100 150 200 250 0 50 100 150 200 250

Phas

e Er

ror (

degr

ee)

Pole Number

Pole Number Pole Number

3.2o 4.7o 3.3o

Assembling Diff. Adjuster

Precise Gap ControlPrecise Gap Control

Sub-Micron Gap Monitoring

• In order to avoid FEL gain degradation, the gap values of 18 segments should be identical with an accuracy of ~1μm.

• The gap monitoring should be done with sub-micron resolution and be UHV compatible.

Sensor Type Stroke UHV Res. Drift CostLED&CCD ◎ ◎

◎

△

△

△

△

Optical Fiber ○ △

△

△

◎

◎

Mag. Digital ○ ◎ ◎

◎Capacitive × ◎ ◎

Performances of Several Gap Monitors

UHV-compatible Gap Monitor

Digital Gauge (SONY MS)

UHV-compatible Gap Monitor

Digital Gauge (SONY MS)

Modification for UHV

Target (hard metal)

UHV-compatible Gap Monitor

3.50 3.52 3.54 3.56 3.58 3.60

-0.2

-0.1

0.0

0.1

0.2

Gap

Dev

iatio

n (μ

m)

Gap Set Point (mm)

Gap Control TestResolution < 0.2 μm

Status of Undulator Status of Undulator ConstructionConstruction

Construction Status

•XFEL undulator construction has started in Oct. 2008.

•1st Mechanical frame was delivered to SPring-8 in August 2009.

•After field correction & vacuum chamber assembly, 1st undulator segment was installed in the XFEL undulator building in mid-October.

•As of December 2009, 3 undulator segments have been installed.

Installed Undulator

Installation of 3/18 Undulatorshave been completed

Time Table for Mass Production

Production rate: 3 weeks/deviceProduction rate: 3 weeks/device

Summary

•R&Ds for SPring-8 XFEL undulators, such as in-situ magnetic measurement & correction, precise gap monitorings, have been carried out.

•At the moment, 3 of 18 undulator segments have been installed. The installation of all segments will finish next August.