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.