Electron Beam Diagnostic System
for the Japanese XFEL, SACLAIBIC 2012
Oct. 1st, 2012
H. Maesaka, H. Ego, C. Kondo, T. Ohshima,
H. Tomizawa, Y. Otake,
RIKEN SPring-8 Center
S. Matsubara, T. Matsumoto, K. Yanagida,
Japan Synchrotron Radiation Research InstituteOct. 1st, 20121

Outline• Introduction– Current status of SACLA• Design and Performance of Beam Diagnostic
Instruments and their application for beamcommissioning– RF-BPM and Multi-Strpline BPM– Screen monitor (OTR, YAG:Ce, Desmarquest)– Fast differential CT– Coherent radiation monitor to estimate thebunch length– Streak Camera– C-band Transverse deflector cavity• SummaryOct. 1st, 20122

Introduction

•

SACLA

•

8 GeV Linac and in-vacuum undulator beamline•

We started beam commissioning in March 2011 and observed the first
XFEL radiation in June 2011.
Public user experiments have been performed since March 2012.

•– SPring-8 Angstrom Compact Free Electron Laser– XFEL is generated by Self-Amplified Spontaneous Emission (SASE)– CeB6 thermionic electron gun (500 kV, εn: 0.6 mm mrad)– Velocity bunching and 3 bunch compressors to achieve > 3 kA peak current– C-band high-gradient accelerator (> 35 MV/m)– Short period in-vacuum undulator (λu : 18 mm)– Total facility length is 700 m.

– Photon Energy: 5 – 15 keV– Wavelength: 0.08 – 0.25 nm

Oct. 1st, 2012

3

XFEL Spectrum and Profile~ 0.5mm
K=1.8
E=7 GeVTransverse Profile
Narrow band width andhigh brightness
Oct. 1st, 2012

4

XFEL Gain Curve○• Nonlinear amplification• Large power fluctuation in the amplification stage• Small power fluctuation after the saturation
Oct. 1st, 2012

5

XFEL Intensity Stability (24 hrs.)• Photon energy: 10 keV (Wavelength 0.124 nm)• Electron beam energy: 7.8 GeV• Bunch Charge: 0.2 nC
Oct. 1st, 20126

Beam Diagnostic System•

RF cavity BPM (RF-BPM) with position resolution < 1 μm.

••

Multi-stripline BPM for dispersive part to monitor the beam energy
Screen monitor (SCM) with less than 10 μm resolution.

•

Fast differential current transformer (CT)•

Coherent radiation monitors•

Streak Camera•

C-band transverse RF deflector cavity system (RFDEF)– Electron beam must be overlapped with x-rays within 4μm in the undulator section.

– Transverse beam profile measurement, emittance measurement etc.
– OTR, YAG:Ce or Desmarquest screen with high-resolution imaging system.
– Bunch length measurement in the injector part
– Bunch charge monitor without common-mode noise.

– Coherent transition radiation (CTR) and coherent synchrotron radiation (CSR) monitor– Resolution: 300 fs– Resolution: 10 fs.
– Bunch length is compressed to 30 fs.

Oct. 1st, 2012

7

RF Cavity BPM• TM110 dipole mode of Beam-induced RF field is used.

𝑉 = 𝑉1 𝑞𝑞𝑒 𝑗(𝜔𝜔+𝜙)−𝑡/𝑇• TM010 cavity determines the phase reference and the beam charge.

𝑉 = 𝑉0 𝑞𝑒 𝑗(𝜔𝜔+𝜙)−𝑡/𝑇– Beam arrival timing can be measured.

• Resonant frequency：4.760 GHz (C-band)• H. Maesaka et al., Nucl. Intrum. Meth. A 696, 66 (2012).
Oct. 1st, 20128

RF-BPM Electronics• IQ demodulator to obtain amplitude and phase• Attenuator switch extends the dynamic range to
100 dB– From sub-μm to a few mm• Baseband signals are recorded by a 12-bit or 16-bit
VME waveform digitizer.
Oct. 1st, 20129

Position Resolution of RF-BPM
Y
X

•
•
•
•
•

Position resolution was analyzed for 20 RF-BPMs in the undulator section
Estimated position at a given RF-BPM was estimated from the other BPMs.
Measurement and estimation were almost same. (left plot)
Resolution is defined as the rms of the difference between the measurement
and the estimation.
Position resolution < 0.6 μm (rms) (right plot)– 7 GeV, 0.1 nC

Oct. 1st, 201210

Beam Trajectory Monitored by RF-BPM
Single-shot beam trajectory
Data
Estimated trajectory
Estimated trajectory

Data

Oct. 1st, 201211

Correlation between Beam position and XFEL intensity
Beam

BPM-BL3-0-6 Y

BPM-BL3-0-6 X

0-5 0-6

BPM-BL3-0-5 X

BPM-BL3-0-5 Y• Correlation between the beam position (x,y-axes) and FEL
intensity (z-axis)• Easy to see what trajectory is the best.
• Injection orbit is locked to the best point by a feedback control.

Oct. 1st, 201212

Orbit Correction for Variable Gap Undulators• RF-BPM data is used for the orbit correction fordifferent undulator gap.

– Beam orbit is corrected by steering magnets between
undulators– Feed-forward table of steering magnets is prepared.

• Orbit reproducibility is within 10 μm.
Horizontal

Gap
5.2 mm
4.4 mm
3.7 mmOct. 1st, 2012

VerticalGap
5.2 mm
4.4 mm
3.7 mm13

Beam Arrival Timing Resolution• Beam arrival timing can be measured by the phase of
the reference cavity (TM010).
– Useful to monitor the timing drift of the machine– Experimental users can use this timing data

• Required temporal resolution: < 50 fs• Arrival timing resolution: 27 fs (STD)– Measured by the reference cavities of two neighboring
BPMs in the SCSS test accelerator.
Phase Difference ofTM010 cavities
Sigma:
27 fs(0.046 deg.
of 4760 MHz)

Oct. 1st, 201214

Trend of the Beam Arrival Timing
0.5

Exit of undulator beamline
phase (degree)

600 fs~100m apart0-0.5 Entrance of

undulator beamline
5-1-2

-1

5-1-2 ave16
1-2-2

•
•
•

3/24/12 0:00

date

3/23/12 12:00

3/23/12 0:00

3/22/12 12:00-1.5

3/22/12 0:00

1-2-2 ave16

Drift of the arrival timing is appropriately obtained.
Large drift is due to the rf phase drift in the injector section.
Time difference between the entrance and the exit of theundulator beamline is caused by the drift of the reference timingtransmission line due to the ambient temperature drift.

Oct. 1st, 201215

Multi-stripline BPM

EM simulation•••

Multi-stripline BPM is used at the dispersive part of a bunch compressor (BC),because the horizontal beam size is large.
Beam position at BC is important for monitoring the beam energy.

– 0.1 mm sensitivity is required for the beam energy measurement less than 0.1% resolution.

Five stripline electrodes are equipped for each of top and bottom plane of therectangular beam duct.
– Characteristic impedance: 50 ohm– Stripline length: λ/4 of 476 MHz

Oct. 1st, 201216

Electronics for Multi-stripline BPM• Impulse signal from the stripline electrode is converted to a wave
packet of an rf signal by using a band-pass filter.
• Five signals are combined into one line by means of the groupdelay of other band-pass filters and rf power combiners.
• The rf signal is detected by an IQ demodulator and the baseband
waveforms are recorded by VME waveform digitizer.
• Beam position is evaluated from the center of mass of the peakvoltages of the pulse signals.
Oct. 1st, 201217

Arrival timing, beam energy and XFEL intensity

Trend graphs of the XFEL
intensity, arrival timing
and beam energy

Correlation plots withXFEL intensity

Oct. 1st, 201218

Screen Monitor
•

(YAG)

OTR (stainless steel foil), YAG:Ce scintillator
and Desmarquest targets were employed.
– Target is mounted on a shaft driven by apneumatic actuator.

(OTR)

Oct. 1st, 2012•

Custom-made lens system.

••

Resolution: 2 μm (x4 optics)
Images are taken by a CCD camera andtransferred by CameraLink.

– Some of the profile monitors are equippedwith remote zoom system (x1 – x4).

19

Beam Profiles before BC3
238MHz Exit

~0.4 MeV

BC1 Exit

Desmarquest

Desmarquest

5 mm
Oct. 1st, 2012

OTR

5 mm

5 mm

~30 MeV~800 MeVYAG:Ce(t0.1mm)

5 mm

L-band Exit

~30 MeV

CB01 Exit

BC2 Exit~400 MeV

BC3 Entrance~1400 MeV

OTR

5 mm

OTR

5 mm
20

Coherent OTR after BC3
Intense C-OTR

Ring-shaped C-OTR• Intense coherent OTR was observed after BC3– Bunch length < 100 fs– Stainless steel screen• Target was changed to YAG:Ce– But, C-OTR was still observed from YAG:CeOct. 1st, 201221

Mitigation of C-OTR Problem
φ3mm

t0.1mmt0.1mmYAG:Ce with OTR mask
5 mm
5 mm
•
•
•
•
•

YAG:Ce with
Perforated Mirror

Scattered lightfrom hole edge

3 mm

OTR is emitted forward within ~1/γ radian. 図減らす
Scintillation of the YAG:Ce has no directional dependence.
An OTR mask and a perforated mirror were tried to mitigate the C-OTR problem.
C-OTR from the YAG screen is removed from the mask or the hole on the mirror.
Details will be presented later– MOCC04 by S. Matsubara

Oct. 1st, 201222

Comparison between RF-BPM and Screen Monitor
SCM-BL3-2
3.8GeVSCM-BL3-2
4.5GeVSCM-BL3-2
5.3GeVSCM-BL3-2
6.1GeVSCM-BL3-2
6.7GeVSCM-BL3-2
7.4GeVYAG:Ce with OTR Mask
BL3-2 SCM vs BPM X

0.45

3.772GeV

SCM [mm]

0.40

4.445GeV

0.35

5.263GeV

0.30

6.067GeV
6.667GeV

0.25
-0.05

•

0.00

0.05
BPM [mm]

0.10

0.15

7.437GeV

Beam position from an RF-BPM is consistent with that from theadjacent screen monitor.
– Even if the beam energy, profile were changed.
– Error: < 10 μm (STD)

Oct. 1st, 201223

Emittance Measurement

YAG:Ce with OTR mask

• Q-scanning method(t0.1mm)

𝜎𝑥 2 = 𝛽𝛽 𝐿𝑙𝑄 𝐾 + 𝛼𝐿/𝛽 − 1 2 + 𝜀𝐿2/𝛽

Beam

lQ, K

L

ScreenMonitorσ~ 30 μm
(Minimum)

Normalized vertical emittance: 1.09 mm mrad after BC3 (1.4 GeV)
Oct. 1st, 201224

Fast Differential Current Transformer
Positive port
Ceramic insulator

Magnetic core(µ>10 at 1 GHz)

Remainder
Positive signal

Negative
port

φ22

Negative port

•
•
•
•

Positive port

Negative signal

Pickup coil (1 turn)2 positive ports and 2 negative ports
Oppositely coiled.
Common-mode noise can be subtracted.
Rise time: ~ 200 ps (10 – 90 %)Oct. 1st, 201225

CT Data
BeamchopperGun

CT-476

CT-238238 MHzSHB

476 MHzbooster

Accelerating voltages of
238MHz sub-harmonicbuncher cavity wasscanned.

• Bunch length in the velocity bunching region canbe measured by using raw signals from the CT.
• Bunch length: 400 ps (FWHM) minimum.
Oct. 1st, 2012

26

CTR Monitor
To A/D Converter

RF Detector
Antenna
Rectangular
Waveguide• Coherent transition radiation from a fluorescent screen is
detected.
• By using a cut off of a rectangular waveguide, this works as asingle-shot spectrometer.
• In the injector part, about 10 GHz rf signal is obtained.
– Bunch length ~ 100 ps

Oct. 1st, 201227

Accelerating voltages of 238MHz sub-harmonicbuncher cavity was scanned.
(476 MHz booster was turned off.)

CTR Intensity [arb. Unit]

CTR Monitor Data
>3GHz
simulation>6GHz>12GHz>24GHz238MHz Voltage [kV]• The signal strength has a correlation withthe bunch length.
– Consistent with 1D simulation– Amplitude and phase of the sub-harmonic
cavities can be determined

Oct. 1st, 201228

CSR Monitor••••

CSR (Coherent Synchrotron Radiation)
spectrum has a strong correlation withbunch length.
CSR intensity was measured by a THz
detector non-invasively.
Pyro-electric detector or THz diodeCSR from the 4th bending magnet ofeach bunch compressor is monitored.
Mirror with
Beam HoleCSR spectra (simulation)

1 THz

MirrorViewing Port

Dipole Magnet
THz Lens
Pyro-electric Detector
Oct. 1st, 2012

29

CSR Data
CSR intensity v.s. Charge

CSR intensity v.s. Bunch length~200fs(FWHM)

•
•
•
•
•
•

CSR intensity at BC2 was plotted.
Charge dependence 𝑷 𝝀 ~𝑷𝒆 𝝀 𝑵𝒆 + 𝑵𝒆 𝟐 𝑭 𝝀– CSR intensity is proportional to the squareof the beam charge.

S-Band Acc.

Bunch length ~ 300 fs (FWHM) in the XFEL condition
Phase shift 1deg.  Bunch length change ~ 100 fs
Sufficient sensitivity to the bunch length.

Oct. 1st, 2012

~400fs~300fsError bar: STD offluctuation

Bunch length dependence– S-band phase was shifted to change the bunch length.

BC2

BC2
CSR

30

Streak Camera• OTR light is transported to the klystrongallery and detected by FESCA-200 streak
camera (Hamamatsu).
• For bunch length ≳ 300 fs (FWHM)

Oct. 1st, 201231

Streak Camera Data
0.542 ps (FWHM)
20 ps

0.308 ps (FWHM)
S-band phase +9 degrees

XFEL lasing condition

0.913 ps (FWHM)(S-band phase 0 degree)
S-band Acc.

•
•
•
•
•

BC2

C-band Acc.

BC3

bypassStreakBunch length at BC2 was measured. Camera
BC3 was bypassed.
S-band phase was shifted to change thebunch length.
Each figure shows 50-shot integrated image.
Bunch length of < 1 ps (FWHM) was obtained.

Oct. 1st, 2012

S-band phase +13 degrees

1.42 ps (FWHM)

S-band phase +17 degrees
32

C-band Transverse Deflecting Cavity~4m

Oct. 1st, 2012

~10m

•
•

Electron bunch is pitched by transverse RF field.
RAcetrack-shaped Iris-coupling DEflectioN structure (RAIDEN)•

Resonant Frequency: 5712 MHz••

Backward traveling wave of HEM11-5π/6 mode
Deflecting voltage: 60 MV– To separate x- and y-mode– H. Ego et al., “Transverse C-band Deflecting Structure for Longitudinal Phase
Space Diagnostics in the XFEL/SPring-8 “SACLA”, Proceedings of IPAC’11.
– To obtain higher kick voltage– To fully utilize the C-band accelerator resource– When 1.7m x 2 cavities are driven by 50 MW klystron.
33

Performance of RF Deflector
Deflector ON

Deflector OFF

Beam

100 fsStray lightof COTR

5 mm~ 20 fs FWHM
> 3 kA peak

• Temporal structure of a 1.4 GeV beam was stretched to
50 fs/mm at 10 m downstream of the deflector cavity.
• Resolution: ~ 10 fs• YAG:Ce and OTR mask are used in the profile monitor.
Oct. 1st, 201234

E-t Phase-space Measurement
10 m downstream of RFDEF
t

After switching magnett

E
E

Oct. 1st, 201235

Summary•

RF Cavity BPM•

Multi-stripline BPM•

Beam Profile Monitor•

Fast Differential Current Transformer•

CTR and CSR Monitor•

Streak Camera•

C-band Transverse RF Deflecting Cavity•

By using these instruments, X-ray lasing was achieved at SACLA.

– Position resolution: 0.6 μm– Sufficient sensitivity to the energy measurement at BC– C-OTR was observed after BC3.
– C-OTR was mitigated by YAG:Ce screen with a spatial separation method.
– 1 mm mrad emittance was successfully measured.
– Rise time: 0.2 ns– Bunch length measurement around 500 ps.
– Sufficient sensitivity to the bunch length– 300 fs (FWHM) bunch length was measured– Temporal structure measurement with 10 fs resolution– E-t phase space can be measured

Oct. 1st, 201236

Oct. 1st, 201237

Oct. 1st, 201238

Demanded spatial and temporal resolution to beam
monitors & their numbers

Kinds of Monitor

Number

RF cavity BPM

57

Multi-stripline BPM

4Screen Monitor

43

Differential Current Transformer

30

Transverse rf Deflector

1Streak Camera by using OTR

3

EO Sampling1

Waveguide Spectrometer
CSR Pyro-detector
Oct. 1st, 2012

To keep stable lasing, the beam
monitors must measure a spatial
resolution of less than 1 mm forthe undulator section, a 30 fs
beam pulse width, and a beam
arrival time of less than 30 fs
after the BCs.

4~5
3
39

Detection Principle of RF-BPM• TM110 dipole resonant mode of a pillbox cavity– E-field is linear around the axis

• Output voltage• Need to discriminate in-phase component from
quadrature.
Oct. 1st, 201240

BPM GUI

Oct. 1st, 201241

Imaging System

Ray tracing simulation••

Custom-made lens system
Variable magnification: x1 – x4

– Lens and CCD camera are mounted on a motorized stage– x1 optics: Beam finding– x4 optics: Precise measurement

Oct. 1st, 201242

Spatial Resolution• Spatial resolution of the imaging system
was measured by using a grid distortion
pattern.
• Spatial resolution: 2.5 µm (HWHM)– x4 optics– Consistent with lens simulation

Grid distortion pattern
Oct. 1st, 201243

OTR Target
For frame

For screen• Thin stainless steel foil

– Thickness: 0.1 mm– To reduce radiation damage of other components.
• 1mm-thick frame to support the foil
– Ten 0.1 mm thick foils are stacked and unified by adiffusion bonding technique.

• Surface roughness: several 10 nm• Flatness: 3 µm
Oct. 1st, 201244

Mitigation of Coherent OTR
YAG:Ce with OTR mask
5 mm

t0.1mm• Target was changed to YAG:Ce– C-OTR was still observed from YAG:Ce– Scintillation of the YAG:Ce has nodirectional dependence.

• OTR mask

– 5 mm width– OTR is emitted forward within~1/γ radian.

• C-OTR problem was mitigated by
YAG:Ce and OTR mask.
• Details are presented later

5 mm
Squeezed beam
Masked area
~ 5 mmScintillation COTR

– MOCC04 by S. Matsubara

Oct. 1st, 201245

Perforated Mirror for COTR reduction
φ3mm

t0.1mmYAG:Ce with
Perforated Mirror

Scattered lightfrom hole edge

Beam Image

3 mm
•
•
•

C-OTR

Beam near the hole edge

C-OTR from the YAG screen is discarded through a hole in the mirror.
Only scintillation light is reflected by the perforated mirror.
When the beam is near the hole edge, C-OTR can be observed.

Oct. 1st, 201246

Common-mode Noise Reduction
Beam signal
Common-mode Noise from klystrons
Bottom port (negative)
Remainder
1mV/div, 10µs/div• Common-mode noise was reduced to 1/10.
Oct. 1st, 201247

CT GUI

Oct. 1st, 201248

Fast Gate CCD to Remove C-OTR
•
•
•
•
•
•

C-OTR is prompt radiation.
Decay time of YAG:Ce scintillation is ~ 70ns.
Fast gated CCD camera can distinguish them.
~ 1 ns resolution. (but very expensive…)
First developed at FLASH
M. Yan et al., “Beam Proﬁle Measurements Using a
Fast Gated CCD Camera and Scintillation Screen to
Suppress COTR”, Proceedings of FEL 11, THPB16(2011).

Oct. 1st, 201249

Fast Gate CCD Data

Oct. 1st, 201250

Low-level RF Measurements••

Measured with a 7-cell model.
Pass band•

Shunt impedance– Y-mode is clearly separated from x-mode.
– Bead perturbation measurement– Simulation: 13.9 MΩ/m
– Measurement: 13.7 MΩ/mSimulation

HEM11
X-mode6200
6100

Measurement
X-mode6000

Y-mode5900

Y-mode5800

5712 MHz
5π/6

5700
5600
0

Oct. 1st, 201251

1/6 1/3 1/2 2/3 5/6

1

Beam Arrival Time Jitter observed by the RF Deflector
5/26/2011”
10

Time

9

5mm,

FREQUENCY

87
653 fs/mm

5
4
3
2
1
0

1pps
~ 1.45 GeV

VERTICAL POSITION[um]HISTOGRAM OF VERTICAL POSITION, 100 shots
436.81[um, STD] = 22.7 fs, 53 fs/mm
Oct. 1st, 201252

Parameters of RAIDEN Cavity
Design
60

Data

27.8

Oct. 1st, 201253

Machining of the Cell
• Race-track iris
– Made by a precise milling machine– Electrochemically polished– Surface roughness: 1 µm pk-pk• Other part
– Machined by a precise lathe with a diamondbit– Roughness < 1 µm pk-pk

Oct. 1st, 201254

Waveform of CSR Monitor

μs• THz diode detector: ~10 ns• Pyroelectric detector: ~10 ms

Oct. 1st, 201255

Electron Beam Timing Pick-up using EO Crystal
Timing pick-up
ZnTe electro-optical crystal

By Dr. Tamasaku

 /4
analyzer
 /2

Timing imager
BBO crsytal
800 nm->400 nm

polarizer
 /2

Pulse "stretcher"

Beam

Grating 2

Electric Field E
Grating 1

Disk Shape~1 0 p s

Optical delay

Electric Magnetic Field ofRelativistic Electron Beam
Magnetic Field B
Oct. 1st, 2012

110 fs Ti:Sapphire
56

EO Sampling Results
Courtesy of K. Tamasaku and T. Togashi• ~100 fs resolution is expected
Oct. 1st, 201257

Halo Monitor

Oct. 1st, 2012
Active area

5 mm2

Seen from on the axis

• To reduce the demagnetization of the undulator magnet.
– Undulator magnet can be damaged by beam halo.

• Diamond detector is employed.
– Sensitivity: 10 fC (10–14 C)• Installed into the upstream of the undulator beamline.
58

Electronics of the Halo Monitor

Current signal (V/50Ω)

VME

Signal from upper blade

Signal from lower
blade

Time ( 210nsec/div)(a) The output signal fromthe diamond detector
Oct. 1st, 2012(b) The output signal
from the pre-amplifier.

(C) The waveform stored
at data base.

59

Optical Fiber Beam Loss Monitor• Scattered electrons emit Cherenkov radiation in an opticalfiber.
• The Cherenkov light is detected by a photo-multiplier tube.
• Signal intensity  Amount of beam loss (1pC sensitivity)• Signal timing  Position of beam loss

Oct. 1st, 201260

Electronics of Beam Loss Monitor• Waveform is recorded by a VME
AD board• Beam loss is plotted as a functionof the position.
Oct. 1st, 201261

MADOCA

Oct. 1st, 201262

Event Synchronized Data Acquisition• VME reflective memory board is used.
• In each VME crate, trigger number is counted andthe data is synchronized by using this number.
• MySQL database is used.
• Capable of 60 Hz operation
Oct. 1st, 201263

Image Data Acquisition
Screen Insert

Image tagCamera Selection
Gain Setting

Record / Stop

Zoom

CCD camera••

Trigger

Image data is stored in a NFS storage and image tag information is recorded by
MySQL.
Realtime image is monitored by a GUI

Oct. 1st, 201264