Proceedings of IBIC2012, Tsukuba, Japan

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IMPROVEMENT OF THE SIAM PHOTON SOURCE STORAGE RING BPM
SYSTEM
S. Klinkhieo, P. Sudmuang, S. Krainara, N. Suradet, S. Tesprasitte, S. Boonsuya, P. Klysubun,SLRI, 111 University Ave., Muang, Nakhon Ratchasima 30000, Thailand
Yung-Hui Liu, Hsin-Pai Hsueh, June-Rong Chen, NSRRC, 101 Hsin-Ann Road, Hsinchu Science
Park, Hsinchu 30076, Taiwan
P. Songsiriritthigul, School of Physics, Suranaree University of Technology, Muang, Nakhon
Ratchasima 30000, Thailand
This report describes the improvement of the BeamPosition Monitor (BPM) system of the 1.2 GeV storage
ring of the Siam Photon Source (SPS). Systematic studies
and investigations to improve the machine performance,and storage ring BPM system have been carried out in thelast few years. Major technical problems have been foundand solved. The causes of the unreliability of the original
BPM system were also identified. It was mainly causedby the low quality and improper installation of BPM
signal cables. Detailed descriptions of the replacementwith higher quality (lower loss and better interferenceshielding) BPM cables and implementation of a separate
cable trays for the BPM cables, as well as the work on
BPM electronic board calibration will be described. Themeasurement results before and after the improvement ofthe BPM system will also be presented.

INTRODUCTION
The Siam Photon Source storage ring routinely operates
at 1.2 GeV with a nominal current of 150 mA. The ring
circumference is 81.3 meters. Its lattice is Double Bend
Achromat (DBA). The ring has, among other components,
20 button-type BPMs. [1, 2]
As the number of users increases, so does the demandfor better quality beam. Our first efforts focused oninvestigation and improvement of the existing BPM
system since the BPM is the most important diagnostic
tool for both machine studies and routine machine
operation. In addition, it will be an indispensable part ofour orbit feedback system in the near future. In thebeginning of 2011, major problems of the original BPM
system were indentified and fixed by the machine groupand visiting machine physicists from NSRRC, Taiwan.
The improved BPM system shows reliable performanceand exhibits accuracy of measurement in micron-scale
resolution.
In the following sections, we first describe the status of
the original SPS storage ring BPM system. We thenpresent our work on replacing BPM signal cables andcalibrating the BPM electronic modules. Finally,measurement results before and after the improvement of
the BPM system are presented.

____________________________________________*supat@slri.or.th

ORIGINAL SPS STORAGE RING BPM
SYSTEM
Back in the year 2000, the SPS storage ring was justinstalled and commissioned. The ring incorporated a setof 20 button-type BPMs, with each BPM comprised of aBPM block, position sensors, coaxial cables, and detector
electronics board. The signals from each individual board
were collected and processed by the control system. TheBPM block is directly welded on the storage ring vacuum
chambers without flanges or bellows.

BPM Electronic Modules
The BPM pick-up system uses four electrodes as
position sensors. Beam position is a function of theamplitude difference of these electrodes’ signals. Thesesignals are fed into the BPM electronic modules where
they are processed sequentially to provide simultaneously
two outputs: horizontal (X) and vertical (Y) beam
positions. [3, 4]
The MX-BPM-118.00MHz electronic modules of theBPMs were made by Bergoz Instrumentation. All themodules and data acquisition equipments are distributed
into two groups, the housing of which are located outside
the radiation shielding wall on the opposing sides of thestorage ring (Fig. 1).

(a)(b)
Figure 1: (a) Bergoz BPM electronic module. (b)Electronic device rack.

BPM Cables
The old system uses HUBER&SHUNER GX03272
coaxial cables, with one layer of electromagnetic
shielding, mounted with N-type and SMA-typeconnectors on each end. The BPM electrode signal isISBN 978-3-95450-119-9
Beam Position Monitor System

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

MOPA21

Proceedings of IBIC2012, Tsukuba, Japan

carried by these cables to the local control rack where thesignal processing BPM electronic is located. The lengthsof the cables vary from approximately 20 to around 30
meters depending on the BPM’s location in the storage
ring.
Figure 2(a) shows the GX03272 coaxial cables,
crimped on one side of the cables with N-type connectors(left), and another with SMA-type connectors (right). The
N-type connector connects to the BPM electrode, while
the SMA-type connector connects to the BPM electronic
module located outside the storage ring.
Figure 2(b) shows the original installation of the BPM
signal cables in the cable trench inside the storage ring.
The trench carries all types of the cables, and even
includes cooling water pipes seen in the pictures.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○(a)Figure 3: Installation of the new BPM signal cables.

BPM Electronic Module Calibration
After the new BPM signal cables were installed, it wasnecessary to calibrate all the BPM electronic modules.
Careful calibration was carried out to compensate for thedifference in cable lengths and input powers. According
to the standard calibration procedure provided by Bergoz
Instrumentation [3], the on-board attenuators: A, B, C andD have to be adjusted until the output SDEMOD signal
has minimum level difference, while the X and Y
readings (shown here on two digital multimeters on theleft in Fig. 4) are closed to zero or fall within ± 20 mV.
These conditions ensure that the BPM electronics exhibits
linearity over the whole dynamic range. [3, 4] Figure 4
shows the calibration equipment setup on site using
Bergoz toolkit (table-top test kit: BPM-KIT). [3](b)Figure 2: Original BPM cables and their installation.
It is rather obvious that this was one of the causes of
induced electrical noise and even EMI problem, which
will directly interfere with the BPM signals, giving rise toinaccuracy and unreliability of the BPM system.
Figure 4: Setup for BPM electronic module calibration.

IMPROVED SPS STORAGE RING BPM
SYSTEMAs mentioned in the previous section, inaccuracy of theoriginal SPS storage ring BPMs was mainly caused by (i)the use of low-quality BPM signal cables and, (ii) theassimilation of all the different types of cables in the samestorage ring cable trench.
This section will describe our efforts on replacing theold cables, and recalibrating the electronic modules ofSPS storage ring BPM system.

New BPM Cable Installation
The high level of noise observed in the old BPM cableis due to the fact that it has only one layer ofelectromagnetic shielding. This makes replacing thecables the top priority. Figure 4 shows the installation ofnew BPM cables. We selected HUBER&SHUNER
SUCOFEED cable, which has low loss rate and double
layers of interference shielding. The new BPM cables
were put in their own dedicated cable tray.

IMPROVED BPM MEASUREMENTRESULTS
Figures 5(a) and 5(b) show, respectively, typicalhorizontal (X) and vertical (Y) positions of electron beamin the SPS storage read from BPM no. 18 before and after
installation of the new BPM signal cables.
Before the improvement (original cable), the X and Ypositions exhibit large fluctuation. The maximum X andY changes in 5 hours are about 150 and 170 m,respectively. Here, it is very important to note that theBPM which has rapid change larger than 10m aresorted out as bad BPM. [5]ISBN 978-3-95450-119-9
2Beam Position Monitor System

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now be easily discernable. The results show significant
increase of the BPM performance.

B P M 1 8 -X (o r ig in a l c a b le )- 0 .5 5

CONCLUSION- 0 .6

Position [mm]- 0 .6 50 .4 5
B P M 1 8 -X (n e w c a b le )0 .40 .3 50 .3012

T im e [h o u r ]345(a)-1 .8

B P M 1 8 - Y ( o r ig in a l c a b le )Position [mm]-1 .9

ACKNOWLEDGMENT-2

The authors would like to thank Accelerator
Technology Division and Technical Engineering Division
staffs of SLRI for their technical assistance.

-2 .1

Position [mm]-2 .20 .1
B P M 1 8 - Y ( n e w c a b le )0REFERENCES

-0 .1
-0 .2
-0 .3

The causes of the inaccurate and unreliable BPM
signals of the SPS storage ring have been identified andsolved. The original BPM cables were replaced with
better quality ones, which were relocated to a dedicatedcable tray to minimize interference. Since therecommissioning of the storage ring last year, the moreaccurate BPM system has been instrumental in theundertaking of the machine group to further improve thequality of the beam, as well to setup and implement aslow orbit feedback system.

0123T im e [h o u r ]45(b)Figure 5: The BPM no. 18 reading during the machine
operation.
After the improvement (new cable), the signal
fluctuations of the X and Y positions are drasticallyreduced to only a few microns. Systematic beam drift ofabout 15-20 m, which cannot be observed before, can[1] S. Rujirawat et al., “Improvement of the SPS
Machine Performance”, APAC’04.
[2] P. Klysubun et al., “Operation and Recent
Development at the Siam Photon Source”, APAC’07.
[3] http://www.bergoz.com/[4] K. B.Unser, “New Generation Electronics Applied to
Beam Position Monitors”, Beam Instrumentation
Workshop 1996.
[5] H. S. Kang et al., “Test Result Slow Global Orbit
Feedback using MATLAB at PLS”, Proceedings ofEPAC 2004.

ISBN 978-3-95450-119-9
Beam Position Monitor System

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Position [mm]- 0 .5

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