The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Commissioning of the SPring-S Storage Ring
Haruo OHKUMA, Schin DATE, Keiko KUMAGAI, Mitsuhiro MASAKI, Takamasa
MASUDA, Takeshi NAKAMURA, Jun-ichi OHNISHI, Takashi OHSHIMA, Taihei
SHIMADA, Kouichi SOUTO ME, Shiro TAKANO, Hitoshi TANAKA, Masaru
TAKAO, Kazuhiro TAMURA, Koji TSUMAKI, and Noritaka KUMAGAI
Accelerator Division, SPring -8, Kamigori, Ako-gun, Hyogo 678-12, Japan
Abstract
In ord~ to open the facility to synchrotron radiation users,the Spring-8 storage ring has been und:rgoing beamcommissioning. The COD correction reduces the residue
down to ....0.2 mm in terms of an rms. value in both horizontal
and vertical planes. The beam lifetime of -35 hours or more
has been achieved at the beam current of -20 rnA and a beamdose of 11 Ah. Various machine parameters of the storage ringwere tuned during the beam commissioning. The first stageof the beam commissioning will be completed at the end of
September 1997.
1. Introduction

SPring-8 is the focility of a third generation synclrrotron
radiation source in the Xray region. The accelerator system
consists of an injector linac of 1.2 GeV, a booster synchrotronof 8 GfY and a storage ring of 8 GfY. It will be open to theusers with ten beamlines since October 1997.
Beam commissioning of the injector linac was started on
August 1996. Successively, beam commissioning of thebooster synchrotron was started on December, and the storage
ring was started since March 13th and the first stage of it wassuccessfully completed by accumulating the electron beams ofabout 20 rnA one month later. This quick tuning was
mainly due to the high completion ofhardware. Especially,
the precision of magnet alignment was so high that nosteering magnet was used to store the first beam in the ring.
The major milestones wring the storage ring beamcommissioning are listed Table I.
Table I. Progress of Storage Ring Beam Commissioning
DateMilestones

3/13
3/13
3/14
3/25
3/26
4/17

Start of SSBT tuning
Start of storage ring beam conunissioning
Completion of first tum
Capture of electron beams in RF buckets
First observation of photon beams from a bending magnet
Stored current of 19.6 rnA(lifetime -3 hrs with ID gap fully opened)
Start ofbeamline conunissioning (BL02Bl and· BL471N)
Operation with ID gap of 8 mm
Period of beam self-clearing on vacuum components(lifetime 14-1S hrs at -18 rnA)
Periodical inspection of storage ring by the STA
License by the STA for storage ring operation
Start of experiments at two beamlines
Period of summer shut down

In this paper, tuning of the storage ring machine parameters,
conditioning of the vacuum system with beam self-cleaningand so on, are described
2. Injection
For beam injection into the storage ring four (three DC andone pulsed) septum magnets and four bump magnets are used.
In the early stage of the commissioning the beam was injected
directly onto the design orbit of the storage ring, and a one-tum
trajectory was measured by using beam position monitors.
Since the beam is injected 24.5mm insire from the resign
orbit and bump magnets cannot make this amplitude, steering
magnets were used to make an auxiliary DC bump in theinjection part.
To accumulate electrons in the storage ring, septum andbump magnet strengths were tuned with an off-axis injection
scheme. The auxiliary DC bump was made in the injection
part if necessary to reduce a coherent amplitude. We tried tofind the best parameter set to make injection efficiency as highas possible. At present, the efficiency of 80-90% has beenachieved in the following scheme: in a typical case the bump
amplitude of 16.2mm is made with two bump magnets in theoownstream of the injection point and 14.0mm is mare with
upstream two bump magnets, which means that the bump is
not closed and has a discrepancy of 2.2mm at the injection
point. The auxiliary DC bump is not made in this case.
Since we can select an arbitrary RF bucket among 2436
ones at eoch injection, the filling pattern in the storage ringcan be controlled easily [1]. In an usual multi-bunch
operation partial filling is adlpted. In adition to themulti-bunch operation, single- and several-bunch operations
were tested At present, the maximum current per bunch isabout 4mA, above which the vacuum deteriorates.
3. Tuning of RF system

5/14
5/16
5/17-6/15
6/16-18
7/3
7/12-8/24

There are three RF stations (named B,C and D) arranged
around the ring. Each station has 1.0 MW klystron and 8
single cell cavities at a low betatron straight section.
In the beginning of the commissioning, the RF frequency
is roughly fixed by fitting the initial phase of the synchrotron
oscillation. After the COD well corrected, the RF frequency
was fixed so as to minimize the 48th harmonics of the COD,
which mainly comes from the dispersive distortion caused by·
the energy deviation.
In the early stage of the commissioning, we a<ljusted thephase of the RF stations to make the tum number of the beam
longer and finally to capture it. The preferable phases of theB, C and D stations were -80°, -90° and 85°, respectively.
The total accelerating voltage of 4 MV, which amounted to 12MV. Later, the phases of the RF station were refmed so as tomaximize the synchrotron freq.Jency [2]. The resultant-62-

The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

phases of the B, C, and D stations were -104.5°, -96.7° and85.0°, respectively. After fixing the phases, we calibrated
the accelerating voltages of the RF cavities by measuring thed!pen<blce of the synchrotron frequency on the indivicilalvoltages.

field and the effective length is reruced The agreement
between calculated and measured values were improved bytaking oc.count of these effects, but we still have somediscrepancy shown above.

4.3 Dispersion
4. Measurements of machine Jlaramctcrs

4.1

OpticsThe lattice structure of the SPring-8 storage ring is ofrouble-bend achromat type, and there are 48 straight sections
where the dispersion vanishes. This straight section is used
to install not only insertion devices but also septum magnets
for injection or RF cavities.
During the commissioning period we studied three kinds ofstandard optics: "hybrid", "high~beta" and "high-tune" optics.
In the "hybrid' optics, the horizontal betatron function f3x
takes a large value (about 20m) and a small value (about lm)
alternately in the straight sections (Fig.l), while in the"high-beta" optics Px takes a large value in all straightsections. The "high-tune" optics has a larger value ofhorizontal betatron tune compared with the "hybrid" optics.
Design values of the emittance for "hybrid', "high-beta" and"high-tune" optics are 7, 7 and 5.5nmrad, respectively.

The dispersion function was d:rllced from beam positions
measured at different RF frequencies. In Fig.2 we show theaspersion function of the "hybrid'' optics after COD
corrections. In this measurement the RF frequency wasshifted. by ±50Hz from the central value 508.579373MHz, ama design value of the momentum compaction factor was used.
Residual dispersions in the vertical direction were found to besmaller than those in the horizontal direction.
In Fig.2 we can observe a global modulation of horizontal
dispersion with 3 peaks. Because the ring has 48 cells and thehorizontal betatron tune is around 51, this modulation showsthat the component with harmonic number 51 remains in thehorizontal resiwal dispersion. We observed moddation with
6 (=48-42) peaks in the high-beta optics and with 5 (=53-48)
peaks in the "high-tune" optics.
0.3
0.25
0.2

:§: G.15

Horizontal ~----- Vertical~

40
High-~

r=-"- - - Dispersion

Low-~

t.so
1ii'30"C::.,l~0=80.5'-'e10W~lr~;;: 20

0.1

0.05

I~ I lUI

lliol.l~ll!IUIIIT"1..-, •II"»\ ····ay·0.05

40aouo

160

200

240

210

Serial Monitor Number

Fig. 2. Dispersion for hybrid optics.

4.4 Clromaticity

0 ol.__~~~Lo~-2J_o__,_3_l_o_~4"'-o,---~-::'-:-~--' 0The linear chromaticity was drl.lced from betatron tunes
measured at different RF freqiencies. Typical values for the"hybrid" optics are as follows:

Path Length [m]Table ill Chromaticity for the hybrid optics.

Fig. 1. Hybrid optics.

4.2 Betatron Tune
The betatron tune was measured with the RF knockout
method, and it was found that measured values are always
smaller than resign values. Typical values are listed inTable II.

natural(cal.)corrected(cal.)measuredHv~116.86-40.23

-2.26

-0.63

-0.93

+0.24

Table. II Typical value of the betatron tune.
Hybridcal.
meas.

High-Beta

Both horizontal and verticalchromaticitiesarewell corrected,
but measured values are somewhat larger than calculated.

High-Tune

Hv

Hv

Hv

5. COD Correction

51.30751.25

16.42416.29

42.28142.20

15.37915.28

53.40053_23

20.50020.35

In the commissioning of the SPring-S storage ring, thehybrid optics of which emittance is 7 nmrad was mainly used(see Fig. 1). Natural COD of this optics is small as mentioned
above and rms values of the horizontal and vertical COD are
respectively 1.7 and2.4 mm. Owing to this small COD, even
without any orbit correction, electron beams could be stored in
the ring where both sextupoles andRF system are tumedon.
The COD was successfully corrected by using the ~tcorrector method [3]. At present, the COD can be redlced

In these calculations of the tune, the following two effects
are taken into account: (i) At the edge of bending magnets thebeam passesabout 12.5mm inside from thecenter. Then thebeam feels constant non-linear fiel<E and the tune is shifted.
(ii) A steering magnet set near a quadrupole magnet affect its-63-

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

down to -0.2 mm in arms value. By the COD correction, thehorizontal dispersion is restored markedly and the verticaldispersion is corrected as well [4]. Figure 3 shows thehorizontal COD distribution beforand after the correction.
6 rrrrTT~~~rrrrrr~~~~~rr~
(A)
4'E!

2Q0

u0'3cs -2

L:~

-4

so

100
150
200
Serial Monitor Number

250

300

Fig. 3. Horizontal COD before and after thecorrection.
In respect to stability of the orbit, three kinds of orbit
movement were observed but not cured yet. The first is a orbit
dift of -150 mm occurred after the stop of magnet power
supplies and it continues for about two days from turning on
the power supplies until the temperature of both magnets andgir<b's reaches thermal ecpilibrium. The second is also thedrift caused by a tidal movement and it will be mentioned later.
The last is not a drift but the excitation of COD main
harmonics, i.e., betatron tunes. Amplitudes of the harmonics
slowly vary but an origin of this variation could not be clearly
understood.

COD data exhibited approximate but clear periodic changewith a period of 24 hours. Figure 4 shows the change in thepower of the horizontal zeroth component. Ea::h rot
corresponds to a set of the horizontal COD data. The periodic
change is dsturbed by jumps irentified as changes in
conditions of the beam operation. Also shown in the figure
as a solid curve is the change of a potential of the timgenerating force due to motions of the sun and moon relative
to a local frame fixed to SPring-8 site. The sign of thepotential is chosen so that the smaller the potential, the higher
the rising of the ground we to a red!ction of the local
wavitational acceleration drecting to the center of the globe.
The vertical scale is arbitral for the potential. It turned out·that the phase of the change and relative repths of ravines inthe sequence of data are well reproduced by the solid line. We
therefore conclure that the periodic part of the change in thezeroth component is die to the change in the tire-generating
force at the site of SPring-8. A decrease of lxl0- 10 m in thepower of a positive zeroth component corresponds toapproximately 30 to 40 Jlm <£crease of the radius of theelectron beam relative to beam . position monitors.
Accorc.ing to Fig. 4, an expansion of the ring occurs at thesame time when the ground rises die to the tidal deformation.
If we assume an isotropic expansion of the globe, anexpansion of 30 Jlm in the ring radius of 300 meters
corresponds to a rise of the ground by 60 em, which is a typicalvalue for the earth tide.
0.001250.00100

Jk0.00075

6. Vacuum condition and beam lifetime

The averaged pressure readings of the storage ring are~lxlO-a Pa without electron beam, 5xl0-7 Pa at a beam
current of 18 rnA. After a continuous cleaning by thesynchrotron raciation, the pressure rise die to the photon
induced desorption effect was significantly reduced [5].
An accumulated dose of llAh and a lifetime of 35 hours at
19 rnA current were achieved after four months' operation. The
gap of the insertion revice has been closed rown to 8 mm ofthe minimum gap of the standard in-vacuum type undulator of
the SPring-8, the beam lifetime is reduced due to narrow gap of
the insertion dwice. The relationship of the product of thebeam current (I) and the lifetime (t) versus the accumulated
beam dose can be described by the following formula: Ir ~ 110( JI dt )0· 65 mAh. The trend of the It curve is retermined byscattering of the electron beam. by the photo-resorbed gas
resident in the ring vacuum system.
7. An effect of the earth tide

A change in the electron beam closed orbit in a long time
period has been observed by extracting oscillation modes in
COD from data at a time and tracing them as sequences in time.
To extract oscillations in a space of the betatron phase, theCOD <hta are first normalized by square root of the betatronfunction, for which we have ad>pted resigned values acljusted
for observed tune. The normalized excursion is thendecomposed into Fourier components. Powers of the zerothand the 48th components which are extracted from horizontal.f-0.000500.00025

-2000

2000
4000
time (min)Fig. 4. The power oftbezerothFouriercomponent
estimated from the COD (rot) and thepotential of the tire-generating force (solidline).
8. Conclusion

The first stage of the beam commissioning of the Spring-8storage ring was successfully progressed User service more
will be started since October 1997. In parallel on this mode,
further machine tuning will be made to upgrade performance ofthe storage ring.
References[1] M. Takao, el al., in these proceedings.
[2] T. Ohshima, et al., in these proceedings.
[3] B. Autin, et al., CERN ISR-MA/73-17, CERN, Geneva,Switzerland, 1973.
[4] H. Tanaka, et al., in these proceedings.
[5] H. Ohkuma, et al., in these proceedings.

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