Proceedings of IBIC2012, Tsukuba, Japan

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THE SYNCHROTRON RADIATION DIAGNOSTIC LINE AT SSRF*
J. Chen, Z.C. Chen, Y.B. Leng, G.Q. Huang, W.M. Zhou, K.R. Ye,
SINAP, Shanghai, 210200, China
The synchrotron radiation photon beam line has been
operated since 2009 at Shanghai Synchrotron Radiation
Facility. There are two diagnostic beam lines of thestorage ring behind bending magnet, which is employed
conventional X-ray and visible imaging techniques. A
synchrotron radiation (SR) interferometer using visible
light region in order to measure the small transverse
electron beam size (about 22μm)，low emittance and a
low coupling. A small off-axis mirror is set for theconvenience of the observation. Wave front testing is used
for interferometer to calibrate the deformation effect of
optical components. An X-ray pin-hole camera is also
employed in the diagnostics beamline of the ring tocharacterize beam. Typically the point spread function of
the X-ray pinhole camera is calculated via analytical or
numerical method. Those two methods check each other.
As a result, the measurement with SR system has quite
enough resolution of itself even though the absolute beam
size acquired. This existed system suffices with dynamic
problem for beam physics studies. It has been measured
2.8nm.rad in small emittance mode at SSRF.

measurement equipments such as SR interferometer, x-ray
pinhole and streak camera etc. in this paper. There are thegeneral design of the SRM, extraction mirror design, andmeasurement equipments. Using this monitor, we cancharacterize the electron beam size, phase-space ellipse
and emittance. It will be shown some results also.

INSTRUCTION
The source point of SRM is bending magnet nearinjecting point. The synchrotron light is extracted by awater-cooled beryllium mirror. Then three mirrors guidethe light to the dark room. The synchrotron lightinterferometers [2] [3] is set in the dark room and theymeasure horizontal and vertical beam sizes. Also a
focusing system is applied to obtain the image of beamprofile. The setup of all diagnostic beam line, it is include
interferometer, x-ray pinhole camera and streak camera.

GENERAL OVERVIEWFor SSRF 3.5Gev storage ring, the emittance is 3.9(nm.rad). The Beam profile size, horizontal σx is 53μm
and vertical σy is 22μm by the use of 1% vertical
coupling. The monitor should be able to measure a smalltransverse beam dimension and motion.[1]So
interferometer is one of better equipment to measure this#order beam size. It is located at the 30 end of the 2
bending magnet of the first cell in the ring. A unique
diagnostics line has been working. We also have imaged
the beam profile at the SSRF using x-ray synchrotron
radiation (XSR) at the (0.8)0 end of same magnet, aselectable pinhole aperture. A unique synchroscan anddual-sweep features of visible streak camera has beenused since 2009. Both transverse beam size and bunch
length have been determined by this beamline.
The vertical opening angle of visible SR is roughly
3mrad. 4mrad opening will be available in the horizontal
direction. The visible part of the synchrotron radiation isreflected by water-cooled Beryllium mirror. Using those
two lines, we can characterize the electron beam size,
phase-space ellipse and emittance. X-ray has been fetcheddirectly from Al window. Synchrotron radiation monitor
measures beam profile and beam size of the synchrotron
radiation light source for performance optimization,
routine operation check and various beam physics study.
It is described those dedicated diagnostics beam lines, andFigure 1: Schematic layout of the Optical Diagnostic
Beamline viewed.
The basic layout and main components of the SSRF
diagnostic beam line are shown in Fig. 1.
About this system detailed described is in the follows.

INTERFEROMETER & APPLICATION
The first mirror is set 9m apart from the source point,
which reflects the visible light by 90° downward.
Thermal distortion of the Be mirror for a given absorbed
heat load by X-rays is simulated using the technique offinite-element analysis. We designed the mirror shapehaving a parabolic shape in the backside. Most of the Xray will pass through the central thin part of the mirror.
The deformation of the mirror has been studied in detailin comparison with other materials. The result shows Be
is best material for the extraction mirror.

___________________________________________*Work supported by Shanghai Institute of Applied Physics

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1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○AbstractMOPB70

Proceedings of IBIC2012, Tsukuba, Japan

Thermal Distortion Analysec 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○A thermal-mechanical analysis with electron beams
show: the thermal distortion values for metals between
00C to 4000C, these effects were especially good in
Beryllium mirrors .The deformation of Be mirror issimulated by ANSYS and XOP for varying the shape, size,and diameter of cooling tube. We fixed outer-dimensionof beryllium mirror is 80mm(wide), 60mm(high),
12mm(thickness). With the diameter of water-coolingtube will 8mm, the centric deformation of mirror surface
results 3.9μm with inlet water temperature 260C. The
highest temperature of mirror will be 560C.
Actually, the key point for interferometer design of themirror is to make deformation smooth and symmetry
about the centre of mirror. It isn’t important forinterferometer that 1 to 2 μm deformation of the mirror.
The Calibration of interferometer has been done with ray
trace technique. So, the beryllium mirror with two coolingtube which haves a parabolic shape in backside is appliedin the SSRF. In the future, two parabolic shape Be mirrors
in the backside, as shown in Fig. 2, can be employ
extraction mirror on the way. One for daily monitors
another one for interferometer measurement. The
deformation will be getting small than one mirror. It will
be install on beam line in the future.

input light. The σ-polarization of SR is selected bydichroic polarization filter. The arrangement of SR
interferometers is shown in Fig. 3. A ray tracing method
using a Hartman square mask is used to calibration of SR
interferometer due to the first mirror deformation. [4]The measuring interferogram is fitted by the intensity
distribution of the form. The image analysis system works
extracting the orthogonal profile, centre position, and leastsquare fit to evaluate the beam sizes.

Figure 3: Arrangement of SR interferometers.
The 800Mb/s interface enables full frame rate and evenmore cameras on the same bus. The IEEE-1394b cablewith jack screws allows a more secure connection to thecamera. 12-bit A/D converter, Via external trigger,
software trigger (on same bus), This equipment has beentested and found to comply with the limits for a Class A
digital device, have good linearity It provide reasonable
protection against harmful interference when theequipment is operated in experimental environment.
After all environments and system calibration,
Interferometer is good enough for the measurement of afew μm small beam size.

Low Emittance Measurement

Figure 2: The construction of two Be mirrors.
Motor control can help us to select mirror. Small
deformation place will be fetching light. The Point Grey
Flea®2 is designed to have the form factor of similarindustry standard analogy cameras to get interferometer
pattern.
Two
Harsherian-typereflectiveSRinterferometers are installed to measure the both ofvertical and horizontal beam sizes. The double slit is set at
18 meter apart from source point. A focusing mirror,
f=2000mm, is used as an objective mirror. A small offaxis diagonal mirror is set for the convenience of theobservation. A band-pass filter, which has 50nm or 80nm
bandwidth at 550nm, is used to limit the wavelength of

The very low effective emittance optics of SSRF isfound out by the method of Multi-Objective Genetic
Algorithm (MOGA). [5]The main function of interferometer is to measure thebeam profile size needed in the calculation of theemittance beam section size，calculated emittance fromfollowing formula (Eq.1),

6 ( width 2  D 2 (emittance=

dp 2
) )
p

B

D

the dispersion function

dpp

momentum dispersion function(1)

B
beta function
Width beam width
So we can get emittance from beam size.

ISBN 978-3-95450-119-92Transverse Profiles, Screens & Wires Monitors

Proceedings of IBIC2012, Tsukuba, Japan

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Table 1: Beam Parameters of the Low Emittance at SSRF
Mode A

Mode B

Tune (H, V)

23.313, 11.232

23.309, 11.238

Natural emittance / nm.rad

3.4±0.2

2.9±0.2

design emittance / nm.rad

3.51

2.88

Natural chromaticity (H, V)-58, -17-67, -23

Corrected chromaticity (H, V)

1.5, 1.0

2.0, 3.0

Momentum compaction factor(4.1±0.2)×10-4(4.2±0.2)×10-4

Synchrotron frequency

0.0073±0.0002

0.0074±0.0002

Coupling

0.4%

0.5%

Beam current / mA

210

210

Beam lifetime / hrs

16.5

15.0

Injection efficiency

>90%

~50%

RMS beta beatings (H, V)

0.6%, 0.7%

0.7%, 0.8%

Interferometer is used to acquire beam size in order todetermine the extent and study to get small the emittanceat SSRF. The measured beam parameters in 2011 aresummarized in Table 1. For mode A the design emittanceis 3.51 nm.rad, measured natural emittance is 3.4±0.2.
Also for mode B the design emittance is 2.88nm.rad,measured natural emittance is 2.9±0.2 , which shows agood agreement with theory.
It is useful to solve how much is the available lowest
emittance and thus increase photon brightness.

Adjusting Transverse Feedback
SSRF has been operated for users’ experiments since
May 2009. Transverse feedback system is useful to keep
beam instability. The interferometer is used to watch theeffect of transverse feedback system. The beam size
measurement also used to adjust the transverse feedback
system for SSRF storage ring. It is shown as in Fig. 4.
When beam current is getting higher than 40mA, thevertical beam size is getting large. If beam current
changes from 40mA to 100mA, the vertical beam size
will be getting larger from 35 um to more than 100 um.
When the multi-bunch transverse feedback is work; thevertical beam size becomes smaller and stable. The
observed beam size with transverse feedback is 35 um justsame as in the low current. The variation is observed forx, y coupling parameters from those measurements. It isbenefit for the adjustment phase of transverse feedback
system.

(a)(b)
Figure 4: (a) the interferograme and beam image variation
for feedback on or off; (b) X and Y beam size variation
for feedback on or off.

X-RAY PINHOLE IMAGING
Pinhole cameras provide a well known means to image
the light of synchrotron radiation in the x-ray regime. The
basic layout and components of the SSRF pinhole camera
are shown in Fig. 1.
The X-ray beam from the bending magnet, alternatively
the pinhole is installed after the aluminum window, whichtransmits only the high energy photons from vacuum toair. Putting the pinhole assembly outside the vacuum
chamber simplifies design and maintain of the beamline
but sacrifices achievable resolution.
The point spread function was found by summing over
all wavelengths and was fitted with the Gaussian curve.
The resultant rms width was used as the resolution of thesystem [6].
A pinhole array combined by two sets of tungsten slits,
in horizontal and vertical directions, is placed behind theAl window, as close as possible from the source, 6.19 m
in our case. The X-ray image of the pinhole camera wasconverted into a visible light image at peak wavelength of
530 nm with a YAG screen (thickness: 400 μm). The
screen is placed at 9.25 m away from the pinhole, so thatthe image is magnified by a factor of 1.5 [7]. There areusing a YAG/Ce crystal to convert the X-rays to visible
light, A small Si mirror reflect image to CCD camera.
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3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Parameter / unit

MOPB70

Proceedings of IBIC2012, Tsukuba, Japan

Then this is read out through an optical system and a
CCD camera.
A block of 1mm-10mm variable wedge shaped copperis attenuator. It can move up and down by step motor tochange attenuation values to select different energy X-ray.
A macro-lens 2.8/50 and a compact IEEE 1394 CCD
camera get image from YAG screen scintillator. It has an
80-ns response time and be recorded by a CCD camera.
An online video digitizer processes the data at a 30 Hz
rate.
Fig. 5 shows the beam size comparison of calculationand measurements. It is obvious that the experimental
data has good agreement with modelling data, which
verifies the good usability and reliability of SSRF X-ray
pinhole camera.

better resolution can be achieved. Precise calculation orcalibration of the point spread function of the wholesystem is required in this case [9].
By varying the beam size S at the source point andmeasuring image size ∑, the practical Ssys can be derived
from Eq.4 using least-square fitting method.

 D  ( s ) 2  S sys 
 d


1/ 2

(4)

A new beam based calibration method had beendeveloped in the SSRF storage ring.
The high level physical application environment has
been set up and done the online test of device control
using MatLab and middle layer with the SSRF centre
database.

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Copyright ○STREAK CAMERA

Figure 5: Comparison of calculated beam size andmeasured beam size.
The performance of the measurement of the transverse
electron beam size is given by the width of the point
spread function (PSF) of the X-ray pinhole camera. The
contributions to the PSF width are the PSF of the pinhole
itself due to diffraction, and the PSF of the X-ray camera.
The widths of these two contributions add quadratically tothe total resolution of the X-ray pinhole camera, in theapproximation of a Gaussian PSF.
Let A is the aperture of a rectangular shaped pinhole.
The contribution of the diffraction for a monochromatic
photon beam of wavelength is given analytically byformula (Eq. 2).

S diff 

12  d4 A(2)

A simple geometrical computation shows that Saper can be
expressed as formula (Eq. 3) [8],S aper 

A Dd
12 d

(3)

d is the distance from source point to pinhole.
D is the distance from pinhole to screen.
X-ray pinhole cameras are widely used due to simple
setup and high practical reliability. Typically a pinhole
based emittance monitor has a limited resolution of > 10
μm. Recent calculations taking into account the spectral
distribution of the source and applying numerical methods
to precisely evaluate the diffraction have shown that withthe correct choice of pinhole size and magnification a

Bunch length measurements is performed with a streak
camera (HAMAMATSU C5680) that uses a scanstreaking of 125MHz (1/4 RF) and also dual timestreaking is available. As shown in Fig. 1. The attainable
phase stability is good: less than 2ps, and a bunch
separation of 2 ns, while the revolution frequency is 694
KHz. The synchroscan unit operates at 125 MHz allowing
the bunch train to be analysed bunch-by-bunch, evenbunches on one sweep and odd bunches on the returnsweep. The temporal resolution of the synchroscan unit isless than 2ps which will allow an individual bunches to beresolved clearly and analyzed.

Figure 6: The drifting between bunches while beam
injection.
Fig. 6 shows the drifting of bunch to bunch when beam
injection in 10 seconds. Streak camera represents the
temporal profile of the light impulse. Diagnostic beamline receives visible SR from a standard dipole magnet.
Bunch length measurements are made by imaging thesource onto the input slit of a dual-axis Hamamatsu
C5680 streak camera. It will be benefit to study beam
instability, combining with the analysis of anotherdiagnostics monitors.

DATA ACQUISITION AND CONTROL
Application software is located at workstation /Unix
and PC/Linux control console, supporting commercial
software Matlab and LabVIEW.
PXI IOC software can be separated into two parts. The
first part is LabVIEW low level application, which isdeveloped in house, to complete raw data acquisition andISBN 978-3-95450-119-9
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Proceedings of IBIC2012, Tsukuba, Japan

CONCLUSIONSPreliminary commissioning of the SRM is performed;
the glass window has been used to overcome the effect of
air flow. The linearity between electron beam intensity
and radiation image intensity in such system is good.
Accompany with neutral density filter. The dynamic
range can be extended to 103 and with excellent linearity.
The SR monitors measure the beam size, and bunch
length etc. Beam size of electron in storage ring has beenachieved. The transverse RMS beam sizes in bothhorizontal and vertical direction are measured in the rageof a few mA to 200mA by synchrotron radiationinterferometer successfully. The results of vertical beam
size measurement for beam regulation. When beam
current is 200mA, using a wave length λ = 550nm, withacquired data 600 times, the observed horizontal beam
size is 52.3±0.4um and it is good agreed with designed
value. The observed vertical beam size is 34.3±0.4um,
and it is stable with transverse feedback system. From
this observed vertical beam size, eminttance coupling is
1.2%.
The very effective emittance 2.9±0.2nm.rad of SSRF
was found, when coupling is 0.5%, by SR interferometers
to measure the beam sizes.
The X-ray pinhole camera is an imaging system toobtain a profile of electron beam normally and its point

spread function has been calculated via analytical or
numerical method. Interferometer and x-ray pinhole
camera, those two methods check each other in theoperating.

ACKNOWLEDGEMENTS
The authors would like to thank everyone who
contributed to this design through discussions andsuggestions. In particular ，we appreciate T. Mitsuhashi
supports and advices for the constructing this system. The
authors express thanks for discussing with physical groupcolleagues. The support provided by the Technical
Services Division in particular the colleagues in themechanical, vacuum, alignment and control groups.

REFERENCES[1] T. Mitsuhashi, “Beam Profile and Size Measurement
by SR Interferometer” in Beam measurement, Ed. by
S.Kurokawa, et al., P399-427, World Scientific (1999)[2] T. Mitsuhashi, “Measure of Small Transverse Beam
Size Using Interferometer” DIPAC 2001, P26-30.
[3] Y. Yamamotoa, I. Sakaib, T. Mitsuhashic, D.
Amanod, H. Iwasaki, “Interferometric measurementof the beam size in the compact storage ring,” Nucl.
Instr. and Meth, A467–468 (2001) P921–924[4] K.R.Ye, Y.B.Leng, J.Chden, etc., “Synchrotron
Radiation Monitor and Mirror at SSRF,” Proceedingsof DIPAC09, P381-383 Basel, Switzerland[5] S. Q. Tian, B. C. Jiang, M. Z. Zhang, J. Chen, and etal, “Design and commissioning of the very low
emittance optics in the SSRF storage ring,” IPAC
2012
[6] Preliminary Design of Pinhole Camera for NSLS-II
Project, BNL-82324-2009-CP[7] Leng Yong-Bin et al., “The beam-based calibrationof an X-ray pinhole camera at SSRF, ”2012 Chinese
Phys. C 36 80[8] P. Elleaume, C. Fortgang, C. Penel, et al.,“Measuring beam sizes and ultra-small electron
emittances using an X-ray pinhole camera,” J.
Synchrotron Rad. 2 (1995)[9] C. A. Thomas and G. Rehm, “Pinhole camera
resolution and emittance measurement”

ISBN 978-3-95450-119-9
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5c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○signal processing. The second part is the Shared Memory
IOCcore and SM LabVIEW library, which is developed
and maintained by SNS/ORNL, to implement theinterface between low level LabVIEW application and
EPICS CA server.
A LabVIEW and shared memory IOC core techniquebased application has been developed to control thecamera and communicate with the control system through
EPICS CA protocol. The x and y position of the CCD,
and the x and y position and angles of the pinhole arraycan be remotely adjusted. On the optical path, second andthird mirror also can control for synchrotron radiation
light fetch.
The timing card (Event receiver) is a standard VME bus
module used by many laboratories, which driver package
is supported by EPICS community. It has been worked for
streak camera trigger control.

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