PROGRESS ON THE COMMISIONING OF
THE SIAM PHOTON SOURCE
S. Rujirawat, N. Sanguansak*, S. Rugmai, R. Apiwatwaja, G.G.Hoyes, K. Hass,G. Isoyamaa ,W. Pairsuwan and T. Ishii
National Synchrotron Research Center, P.O. Box 93, Nakhonratchasima, Thailand.
aAlso at ISIR, Osaka University, Osaka 567-0047, Japan*Corresponding author Tel.: +66-44-217040 ext. 651 E-mail: nuanwan@nsrc.or.thAbstract
Various problems encountered in the commissioningand performance improving work for the accelerator
complex of the Siam Photon Source are reported alongwith their cures. As representative examples, the irregularfloor settlement, the effect of residual gas on the beam
lifetime and undesirable noise are described. Since theoriginal components were built about 15 year ago, we
have found various problems inherent in an old and usedmachine and also in the infrastructure of the area duringt h e cour se of c om pon en t st or a ge an d m a ch in e
commissioning. Experiences made here provide us with
useful examples of trouble shooting covering various
fields of accelerator technology.

1. Introduction
The Siam Photon Source (SPS) is a light source
accelerator complex, major of which has been transferredfrom the SORTEC Laboratory. The high energy beamtransport line and storage ring have been rebuilt andmodified to have a more advanced structure for theutilization of synchrotron radiation. The main parametersof SPS storage ring are summarized in Table 1. After theconstruction and installation period, the beamcommissioning of SPS started in October 2001. The 1.0
GeV beam was stored successfully in December 2001.
At the beginning, the progress of increasing stored
current proceeded slowly. This was ascribed mainly touneven floor settlement and instabilities of the electricity
and water supplies[1]. The vertical level difference wasmeasured to be as large as 4.0 mm, that is considered tobe very high for a ring of 81.3 m circumference. In July
2002, the realignment of storage ring was conductedwithout breaking UHV[2]. With help from Spring8’s
magnet group, the magnet vertical positions were broughtback to the level with the required precision. Immediately
after the realignment, the commissioning was resumed.
The 1.0 GeV beam was re-stored within 1 month and thebeam current increased gradually. In February 2003, astored beam current of 155 mA was recorded. Withsufficient beam currents, the measurement of several
beam parameters such as betatron tunes and COD shifts
could be implemented. The beam lifetime increased also
gradually, the accumulated beam dose became higher.
In this paper, the current status of the SPS’s machinecommissioning especially the performance of the 1.0 GeVelectron storage ring (STR) after the realignment, andsome result from machine study will be described.
Table 1Main parameters of storage ringElectron energy, E
1.0 GeV
Circumference, C
81.3 mMagnet lattice
DBA
Superperiodicity
4Long straight sections
7 m x44.76, 2.83
Betatron wave numbers; νx , νyRF frequency, fRF
118 MHz
Critical energy of synchrotron radiation, εc 798 eV
0.94,0.15mm
Beam sizes; σx , σy2. Result from the realignment of
the storage ring
The realignment work of SPS’s STR has been reported
elsewhere[2]. Although the vertical levels were moved
back to the vicinity of the decided level, the horizontal
positions of some multipole magnets from SORTEC
could be moved owing to the displacement of the top
target holes. This magnet displacement cannot bedetermined precisely since we moved magnets withcaution against breaking the vacuum of the STR vacuum
chambers during the period of realignment. Similarly, thelocations of beam position monitors (BPM) cannot bealigned perfectly. In order to re-store the beam, several
steering magnets had to be excited with large current. In
addition to the maximum beam current of 155 mA, thebeam lifetime was recorded to be about 50 min at 100 mA.
The injection efficiency was also improved by theadjustm ent of the ma gneti c fi eld paramet ers ofsynchrotron (SYN) and high energy beam transport line(HBT). The inaccurate positions of multipole magnets
could cause the electron trajectory to have large deviationfrom the ideal orbit. As a result, we observed very large
COD ((∆x(s))rms ≈ 3.6 mm, (∆y(s))rms ≈ 1.8 mm) for theelectron trajectory in STR. One possibility is themisaligned horizontal positions of some quadrupolemagnets. The analysis of current–lifetime data alsosuggested the occurrence of the scraping process. The
possible inaccuracy of the alignment of BPMs could also
lead to the observed large COD. In the case where large

COD exists, it is impossible to use sextupole magnets formaking finer beam correction. This prevents STR tooperate at its best performance. Figure 1. shows thechange of the STR beam current during one day inDecember 2002. At this stage the beam lifetime was notlong and the beam dump occurred from time to time.
Thus, the major effort has been focused on the CODcorrection and the beam-based alignment. However,

sever al pr obl em s im peding th e pr ogr ess of th ecommissioning such as power line instability, room andcooling water temperature fluctuations must be resolved
at the same time. The goal of the next stage is to improvethe beam stability and bring the beam lifetime up to thevalue that experiments can be carried out with highprecision.

Figure 1. STR beam current within a day in December 2002.

3. Measurement of beam parameters
To improve the machine performance, measurements ofsome of the beam parameters must be carried out. STR
machine studies have been performed during the last threemonths in 2002. This included the measurements ofbetatron tunes. To measure the tunes, an RF tracking
signal was fed through a strip line RF-KO system and thebeam signal picked up by strip lines were analyzed by aspectrum analyzer. To distinguish the vertical tune fromthe horizontal tune, a telescope with a filter was used toobserve the beam shape directly. The observed beam
shapes and the working diagram are shown in Fig 2. The
betatron tunes were measured to be νx = 4.83, νy = 2.77
for the most stable condition. This values are not muchdifferent from the designed values of νx = 4.76, νy = 2.83.
However, several sources of instabilities exist. They makethe betatron tunes shift during the operation and the beam
moves suddenly. This reduces the beam lifetime and thebeam dumps eventually.

4. Beam lifetime and photon beam dose
Apart from the beam instability effect described in theproceeding sections, the lifetime of the electron beam ismostly determined by the scattering with residual gas
molecular ions in vacuum chamber. They emerge out ofthe vacuum chamber wall when the wall is irradiated withsynchrotron radiation. In the early period, when the beam
was stored in the STR, the pressure was enhanced rapidly
through the photodesorption process. This limited theinitial stored beam current to a value below a few
milliamperes. As the injection efficiency was improved

Figure 2. Left: 1.0GeV beam shape, Right: working
diagram.

and the beam dose increased, the stored current andlifetime increased gradually. Figure 3. shows the plot of
the product of beam current and lifetime versus theintegrated beam dose. From the data, the trend that thelifetime increases is roughly expressed as y = 449.71x0.645
where y is a current-lifetime product and x is theintegrated dose. This is similar to the published data of
the other storage ring[3],[4]. The instabilities arising fromdefects in hardware and environment such as coolingwater temperature fluctuations, and noise prevent thelifetime improvement.

Current*Lifetime (mA*min)

100000

10000

1000

100

100.1

1

10100

1000

Dose (A*h)

Figure 3. Plot of the beam current-lifetime product versus integrated beam dose

5. Trouble shooting

References

Various problems to cause the beam instability in STR
have been found during the commissioning. Some ofthem have been removed. Some hardware defects havebeen found in several parts of the accelerator system
including the pure water supply, the air conditioning
system, and the internal and external noise affecting themagnet power supplies and the machine operation control
system. As the measures for occasional power failuresand voltage fluctuations in the primary line, several piecesof UPS with a large capacity were installed. A new
independent power plant exclusively used by SPS willsoon be constructed. The inappropriate design of thewater cooling system gave rise to difficulties incontrolling magnet temperature. The temperaturefluctuates along with the outside ambient temperature andheat generated in the machine. This caused fluctuations inmagnet current and has affected the beam position in STR.
During the beam injection to STR, noise from the linac
varied current in some quadrupole magnets and steering
magnets. At present, the work for cures of the problems isunderway.

[1] W. Pairsuwan, R. Apiwatwaja, G. Isoyama, S.
Rugmai, S. Rujirawat, N. Sanguansak and T. Ishii, “TheCommissioning of the Siam Photon Source”: Proceedingsof N. International (workshop) on Personal Computer andParticle Accelerator controls, Frascatti, Italy, October
2002.
[2] N. Sanguansak, S. Matsui, S. Rujirawat, R.
Apiwatwaja, S. Rugmai, S. Prawanta, A. Kwankasem, T.
Angsuwattanakul,
S. Boonsuya, S. Srichan, P.
Tarawarakarn, W. Phacheerak, S. Siriwattanapaitoon, P.
Chanpuang, T. Ishii and W. Pairsuwan, “Realignmentmagnets of Siam Photon Source storage ring”: IWAA’02,Hyogo, Japan, November 2002.
[3] S. Hashimoto, A. Ando, Y. Shoji, S. Miyamoto, Y.
Fukuda, H. Ohkuma, H. Saeki and N. Kumagai, Nucl.
Instr. and Meth. A, 2001, pp.145-147[4] C.C. Kuo, H.P. Chang, M.H. Wang, W.T. Weng,EPAC, 1996, pp. 697-699

6. Conclusion
The progress of work for the performance improvementof the Siam Photon Source is summarized. To remove
troubles arising from uneven floor subsidence, the storage
ring was realigned. The 1.0 GeV beam has been stored in
STR up to 155 mA. The beam lifetime has improved
gradually with increasing beam doses following a normal
trend line. Works for noise removal and stabilizing
temperature fluctuations in cooling water is underway.