Proceedings of IBIC2012, Tsukuba, Japan

MOPB63

EMITTANCE MEASUREMENT USING
X-RAY BEAM PROFILE MONITOR AT KEK-ATF
T. Naito*, H. Hayano, K. Kubo, S. Kuroda, T. Okugi, N. Terunuma, J. Urakawa, H.R. Sakai,
N. Nakamura High Energy Accelerator Research Organization(KEK), Tsukuba, 305-0801, JapanThe X-ray profile monitor (XPM) is used for the beam
size measurement in the KEK-ATF dampingring(ATF-DR) at all times. The XPM consists of a crystal
monochromator, two Fresnel zone plates(FZPs) and X-ray
CCD camera. Two FZPs make the imaging optics. The
design resolution of the selected wavelength 3.8nm is lessthan 1µm, which is sufficiently small for the emittancemeasurement of the ATF-DR. However, the measured
results at the early stage were affected by the mechanicalvibration. This paper describes the improvement of theresolution and the measurement results.

INTRODUCTION
The damping ring(DR) of the KEK-ATF has been
designed to produce extremely low emittance beam for
future accelerator technologies, especially focus on theInternational Linear collider(ILC).[1][2] The beam energyis 1.3GeV. The design horizontal emittance(εx), we call“emittance” as “un-normalized emittance”, at a zerocurrent is 1.1 x 10-11m. The vertical emittance(εy) is
1x10-11m when assuming 1% coupling. The expectedbeam size for the vertical is 5.5µm, at the location of thebeam size monitor. The beta function at the location is 3m
for the vertical. The beam size monitor needs to haveenough resolution for 5.5µm measurement. The recent
tuning effort of the DR is aiming to reduce the verticalemittance less than 1x10-11m. In this case, the verticalbeamsizereduces
to4µm(εy=5x10-12m)
or-123µm(εy=3x10 m).
The X-ray profile monitor(XPM) was constructed by
Tokyo University group[3][4] to measure the beam size inthe DR. The XPM is a long-distance X-ray microscope,
which consists of a crystal monochromator, two Fresnelzone plates(FZPs) and an X-ray CCD camera. The X-rayof the synchrotron radiation from the bending magnet ismonochromatized by a crystal monochromator with thewavelength of 0.38nm(3.235keV). The two FZPs
constitute imaging optics and the magnification ratio fromthe source to the CCD camera is 20. The estimatedresolution of the XPM is less than 1µm, which is enoughto measure the vertical DR emittance. The detail of thedesign parameter and the specification of the FZPs aredescribed in [3].
At the beginning of the system commissioning, themeasured beam size could not be less than 6µm in
vertical, which correspond to 1.2 x 10-11m of the verticalemittance. However, the emittance evaluated from other____________________________________________*Work supported by US/Japan Sci. and Tech. Collaboration program.
#takashi.naito@kek.jp

beam size monitors, a laser wire profile monitor(LW)[5]and a SR interferometer(SRI)[6] was less than 1.0 x
10-11m. We investigated the reason of the discrepancy
among the XPM, the LW and the SRI. We found that themechanical vibration of the crystal monochromator
deteriorated the minimum spot size. The minimum beam
size 4µm was measured after reduced the mechanicalvibration.
A standalone video analyser was used, which didn’t
have an interface to connect the accelerator control
system. To synchronize the beam profile data with theother DR parameters, an online video analysis system wasconstructed. The new video analysis system can becontrolled from the accelerator control system and canmonitor the beam profile synchronized with the othermachine parameters.

SYSTEM DESCRIPTION
The layout of the XPM is shown in Figure 1. The
synchrotron radiation (SR) from the bending
magnet(BH1R.27) located just before the long straightsection is used for the XPM. The SR parameters are
summarized in Table 1.
Table 1: Parameters of the SR of BH1R.27
Beam energy
1.3 GeV
Magnetic field of BH1R.27
0.75 TBending radius
5.4m
Critical energy of the SR
0.816 keVThe SR is monochromatized by a Si monochromaterwith crystal lattice plane Si(220), Bragg angle 86.35°
and spectral resolution 5.6 x 10-5 for the wavelength
0.38nm(3.235keV). The two FZPs (Condenser Zone Plate: CZP, Micro Zone Plate : MZP) make the imaging optics.
The CZP and the MZP have 0.91m and 24.9mm of thefocal length, respectively. The magnification ratio of theCZP and the MZP are 0.1 and 200, respectively.

Figure 1: Layout of the XPM.
The image of the source point is magnified 20 times on
the X-ray CCD. The X-ray CCD camera (HAMAMATSU
C4742-98-KWD) is a direct incident type with aISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○AbstractMOPB63

Proceedings of IBIC2012, Tsukuba, Japanback-thinned illuminated CCD, which has high QE. The
pixel size is 24µm x 24 µm and the pixels are 512 x 512.
The camera head is cooled to -50 °C and keep a highvacuum condition for the low thermal noise. The
minimum exposure time is 20ms and the frame rate is 6frame/sec. The CCD is a full-frame transfer type and theCCD needs a mechanical! shutter to cut off the X-ray
irradiation during the readout of the charge on the CCD.

NEW VIDEO ANALYZER

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○We fabricated the in-house made software based on
the linux library. The new video analyzer software has anetwork interface, which can be controlled from theaccelerator control software. The acquired data (theprofile, the beam size, the intensity, etc.) can be saved tothe database of the accelerator control with the otheraccelerator parameters. The acquisition speed is morethan 3Hz. The normal operation of the ATF-DR is 1.5Hz.
It is enough to acquire all of the shot of the beam. Figure
2 shows the example of the XPM image by the software.
The position control of the XPM image is included in thesoftware. The mover of the MZP can control from thiswindow.

Figure 2: Example of the XPM image using the newsoftware.
By using this software, the all of the beam profile data
could store to the database of the accelerator control
system synchronized with the other parameters. This data
can be used for the beam tuning to minimize the verticalemittance as a real time monitor. The trend graph of theXPM is shown in Figure 3. The DR stored current
measured with the DCCT(blue line) is plotted with theXPM data (the horizontal beam size, the horizontal beam
position, the vertical beam size and the vertical beam
position). The current dependence of the horizontal
beam size can be seen in this graph.

Figure 3: Trend graph of the XPM –DCCT (blue line), thehorizontal beam size(green line), the horizontalposition(light blue line), the vertical beam size(red line)
and the vertical position(purple line) are plotted in thegraph.

IMPROVEMENT OF THE BEAM SIZE
MEASUREMENT
Figure 4 shows the vertical beam size measurement in2005. In the case of the ATF-DR, the beam size is afunction of the bunch current due to the intra-beam
scattering. The lines show the calculation.
Themeasured beam size was around 6µm and was not so clear
the current dependence. It seems the measured beam size
was somewhat limited. The oscillation of the verticalbeam position was observed on the CCD using 1ms fastmechanical shutter [4]. The frequency was 100Hz. It
seemed the vertical profile was smeared by the oscillation
during the exposure time.

Figure 4: Vertical beam size measurement in 2005.
We measured the mechanical vibration of eachcomponent. The spectrum of the mechanical vibration invertical direction at the Si monochromater is shown in
Figure 5. The red line shows the Si monochromater andthe blue line shows the floor just beneath of the Simonochromater. The Si monochromater had a large peakat 100Hz. We tried to find out the source of the vibration.
Finally, we found two blowers to cool the waveguide of
the RF system caused the vibration. The RF cavities arelocated 2m down stream of the XPM and the two blowers
sit on the floor just below of the cavities. We moved thetwo blowers to 7m downstream of the XPM and inserted
cushions between the blower and the floor. The exhaustsof the blower are connected using long flexible ducts.

ISBN 978-3-95450-119-9
2Transverse & Longitudinal Emittance Measurements

Proceedings of IBIC2012, Tsukuba, Japan

MOPB63Figure 7 shows the fitting curve of the beta function.
The source point of the XPM is as the location of the redstraight line. The contribution of the dispersion function
in vertical direction is negligibly small. The estimatedvertical emittace at the bunch charge of 0.8 x 1010
electrons is 8.6 x 10-12 m.

SUMMARY

Figure 5: Spectrum of the mechanical vibration in verticaldirection at the Si monochromater.
The vertical beam size measurement after treated themechanical vibration is shown in Figure 6. The measured
vertical beam size was 5+/-0.3µm at the bunch charge of
0.8 x 1010 electrons(3.0mA). The current dependence canbe seen in the plot, which means that the XPM does nothave limitted the minimum beam size. The measured
minimum beam size was 4µm at this time.

The XPM is a important monitor to measure theemittance of the ATF-DR. The measurable minimum
beam size was limited by the mechanical vibration of theSi monochromater. The mechanical vibration was comefrom the vibration of the blower to cool the waveguide ofthe RF system. We succeeded to improve the measurable
minimum beam size by removing the vibration source.
The measured vertical emittance was 8.6 x 10-12m.
The online data acquisition is required for monitoring
the accelerator conditions. We fabricated the video
analyser software for the online analysis of the beamprofile and the other accelerator parameters. All of thebeam profile data could be stored to the database of theaccelerator control system synchronized with the otherparameters.

The authors would like to express their thanks toProfessors S.Yamaguchi, A.Yamamoto and K. Oide for
their encouragement.

REFERENCES

Figure 6: Vertical beam size measurement in 2012.

Emittance Measurement
The beta function at the quadrupole magnet is measured
from the strength dependence of the betatron tune. The
beta function at the source point of the XPM is estimatedfrom the fitting of the beta functions among thequadrupole magnets. Five magnets are used for the fitting.

[1] F. Hinode et. al., ‘ATF Design and Study report’,
KEK Internal 95-4, June(1995).
[2] A. Wolski et al., “Configuration Studies andRecommendations for the ILC Damping Ring”,
LBNL-59449, Cockroft-06-04, Feb 2006.
[3] K. Iida et. al., “Measurement of an electron-beamsize with a beam profile monitor using Fresnel zone
plate”, NIM A506(2003) 41-49.
[4] H.R. Sakai et. al., “Improvement of Fresnel zone
plate beam profile monitor and application toultralow emittance beam profile measurements”,
PRST-AB 10, 042801(2007).
[5] Y. Honda et al., “Measurements of electron beamemittance in the Accelerator Test Facility damping
ring operated in multibunch modes”, PRST-AB 6,092802 (2003).
[6] T. Naito et al., “Very small beam-size measurement
by a reflective synchrotron radiation interferometer,
PRST-AB 9, 122802 (2006).

Figure 7: Fitting of the beta function near the source pointof the XPM.

ISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○ACKNOWLEGEMENT