The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

NEW BPM SYSTEM AT UVSOR
K. Hayashi, M. Katoht, M. Hosaka, A. Mochihashi, T. Kinoshita, J. Yamazaki, Y. Takashima,
Institute for Molecular Science, Myodaiji, Okazaki, JapanT. Honda, KEK-PF, Oho, Tsukuba, Japan
S. Koda, Saga University, Honjo-machi, Saga, Japan

Abstract
A new beam position monitor system was successfully
comissioned at UVSOR. New system comprises 16 signal
processing modules produced by Bergoz Co.. Eachmodule gives the beam position as DC voltage. Thesignals are AD-converted and are accumulated in a PC.
The system can measure an orbit in a second withresolution of a few microns. The system has revealed
various types of orbit drift, which could not be observedwith the old system.

1 INTRODUCTIONUVSOR, a 750 MeV synchrotron light source, has beensuccessfully operational since 1983. The UVSOR
accelerator complex consists of a 15 MeV linac, a 600
MeV booster-synchrotron and a 750 MeV storage ring.
To keep the performance of the machine as high as
possible, the aged components have been replaced onebye one, year by year. In FY2000, we have replaced thebeam position monitor (BPM) system.
At UVSOR, we are proposing an upgrade plan [2]. Its
main goal is to provide more brilliant synchrotron
radiation in wider spectral region. The beam emittancewill be reduced by a factor of 6. The number of theinsertion devices will be doubled. After the upgrade, therole of the BPM system will become more important.
Since the orbit drifts would reduce the effective brilliance,
they should be precisely monitored and be cured. To
realize the independent tunings of the insertion devices,
the orbit movement caused by them should be precisely
monitored and be corrected.
In the UVSOR storage ring, 16 BPMs are installed. OneBPM head consists of four button-type electrodes, as
shown in Figure 1. The old system was constructed earlyin 1980's [1]. In this system, the signal from eachelectrode was selected by a coaxial switch multiplexer
system and detected by a linear detector.
It took about one minutes to measure an orbit with theold system. Since the attenuator control of the BPM
signals was not automated, the operator must adjust theattenuation level before the measurement depending on
the beam current. To measure the orbit more precisely
and quickly, we decided to replace the BPM system.

tmkatoh @ims.ac.jp

Fig 1. BPM Electrodes (upper; cross-sectional view,
lower: top-view). They are mounted on the vacuum
chambers at the bending magnets. Totally 16 monitors areinstalled in the ring.

2NEWSYSTEM
The new system comprises 16 signal-processing
modules, which are commercial products of Bergoz Co.
[3]. In these modules, the bunch signals are filtered at theRF frequency (90MHz). The 90MHz signals are downconverted to an intermediate frequency and are amplified
and detected. In the new system, all the electrodes areconnected directly to the modules. There are no switches.
Typical length of the cables is about 15 m. The lengths offour cables for one BPM head are adjusted with anaccuracy of a few em. The modules output two Devoltage signals, which are proportional to the beam
position in horizontal and vertical. They are ADconverted with 16-bit resolution and a cycle of 1 kHz.
The data are averaged over one second to improve theresolution. The data are stored in a PC and sent to themain control system [4].
The standard deviations of the beam position data weremeasured for various values of beam current, as shown inFigure 4. For the beam current higher than 10 rnA, thestandard deviations are smaller than a few microns.

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The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

16 signal processing modules, AD-converters and a PC
are mounted in one rack.
--e---mx
Horizontal.----,-~~....,...,.-----,-~~.,..,..,.,--l~~~=:=--M-D2X--+-- UlXUVSORSTORAGE RING-&--D3X____..._ U4X
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Average Beam Current [rnA]o~~~....___---9-- UIY
Vertical.----,-~~....,...,.---~~~.......- l =:=~~~PER5CJIIAL~DlY-I--U3Y___. CXII'IJTER--t:r- D3Y____.._ U4Y-..-n4Y___._mY

Fig.2 Schematic drawing of new BPM system----+--- DSY

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Average Beam Current [rnA]
Fig. 4 Standard deviations of beam position data
Those for five samplings are shown against various beam
currents. The data from all16 BPMs are shown. Theupper is horizontal and the lower vertical.

3 ORBIT DRIFT
New system has revealed orbit drifts in various timescales. In Figure 5, orbit drifts in a users run are shown.
UVSOR is typically operated for users as follows. Afterthe beam injection, the beam energy was ramped from
600MeV to 750MeV and the orbit was corrected. Thenthe users experiments start. The data in Figure 5 started
also at this moment. There can be seen a rapid drift,
especially in horizontal, during the first ten minutes. In
vertical, there can be seen a slow drift in time scale ofhours. The amplitudes of the drift motions are a few
hundreds of microns.
Fig. 3 New BPM Station-373-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

In Figure 6, another orbit movement is shown. These
data were taken when the temperature control system of
the cooling water was malfunctioned. The temperatures of
the cooling water of the magnets and the vacuum
chambers were fluctuated with amplitudes of about 2
degree and periods of about 10 minutes. This was causedby periodic on and off of the cooling tower. There can beseen orbit movements in horizontal and verticalsynchronized with the temperature changes. The
amplitudes are about a few tens of microns.

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Fig. 6 Orbit movement caused by temperaturefluctuations of the cooling waters for magnets andvacuum chambers
Beam position at one BPM (B3D) is shown.

5 CONCLUSION
The beam position monitor system at UVSOR wasreplaced this year. New system was successfullycommissioned. It is providing a set of beam position data
every second with a resolution of a few microns. It saves
the time for orbit correction significantly. It has revealed
the orbit drift at UVSOR in users operations. Their origins
will be investigated with the beam position data from thenew system. The orbit stabilizing system will beconstructed based on the new system in future.

1 2 3 4 5 6 7 8 9
BPMNumber

5 REFERENCES[1] T. Kasuga et al., Proc. 5'b Symp. Accel. Sci. Tech.
(Tsukuba, 1984), 145[2] M. Katoh et al., Noel. Inst. Meth. A467-8 (2001), 68[3] http://www .bergoz.com[4] N. Kanaya et al., Noel. Instr. Meth. A 352 (1994) 166

Fig. 5 Typical orbit drift observed during a users
operationThe upper is the horizontal data and the lower the verticaldata. The data interval is about 10 minutes.

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