The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

Application Software for Orbit Correction of SPring-S Storage RingHitoshi TANAKA, Schin DATE, Keiko KUMAGAI, Mitsuhiro MASAKI, Takemasa MASUDA,Takeshi NAKAMURA, Haruo OHKUMA, Jun-ichi OHNISHI, Takashi OHSHIMA, Taihei SHIMADA,Kouichi SOUTOME, Shiro TAKANO, Masaru TAKAO, Kouji TSUMAKI, and Noritaka KUMAGAI
Accelerator Division, SPring-8, Kamigori, Ako-gun, Hyogo 678-12, JapanAbstract
Application software for orbit correction of the SPring-8
storage ring has been developed. By using this software,closed orbit distortion (COD) of the storage ring could be
reduced down to - 200 J..Lm in a rms value.

1 Introduction
The storage ring is composed of 44 Chasman-Greencells and 4 straight cells with bending magnets removed,
and its emittance is about 5 nmrad. Such a typical low
emittance storage ring is generally sensitive to magnetic
errors. Large COD was predicted and there was also somepossibility that the injected beams cannot circulate in thering. In such a case, it is necessary to correct the COD byanalyzing beam trajectory data. In order to smoothly
commission the storage ring under any condition, it is thus
important to prepare an orbit correction system having not
only the usual COD correction scheme but also a function
to correct the COD by analyzing beam trajectory data.

corrected by successively superimposing a single kicktrajectory on the first turn trajectory [4,5]. Figure 2
schematically shows this correction sequence. The first turnsteering (FTS) package provides following functions: (1)The FTS correction can be simulated by using an arbitrarysteering magnet, changing the strength of the magnet, withhelp of a graphic system to display an expected result. (2)The least square method is available to calculate the strengthof a selected steering magnet with an arbitrary set ofmonitors. (3) The successive correction is performed semiautomatically with a predefined set of combinations ofmonitors and a steering magnet.

2 Application Software for Orbit Correction
The composition of the developed application software
for the orbit correction is shown in Fig. 1. Major
components are loosely linked via the database. This
distributed structure has an advantage on the modification ofprograms, which is frequently occurred during acommissioning period. In the storage ring, there are 288
beam position monitors (BPMs), 285 horizontal and 283
vertical steering magnets to control the COD less than 100
J..Lm [1].
Machine parameters required for the operation are set by
the operation control panels in a work memory field of thedatabase, which is called a "current data set" [2]. The optics
calculator is available for providing the orbit correction
packages with optical parameters such as betatron functions
and phase advances at all monitors and steering magnets.
According to a choice of measurement-modes, COD or
trajectory data are measured and stored in the database or in adata file by the BPM control panels. These data are used bythree kinds of correction packages to calculate the strengthof steering magnets. The strength can be set from eachcorrection package directly by issuing the command [3] tothe power supplies.

285 Hori. and283 Vert
Steering Magne~

Trajectory
Data COD data~taFiles

2.1 First turn steering package
This is used to correct the COD in the case where theCOD exceeds the aperture of vacuum chamber. The COD is-461-Fig. 1 Composition of orbit correction system.

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997x,y
1st Crrrection Step

2nd3rd4th ....

s.....
Mmitoringfor SlMrn.itoring Mmitoring Mmitoringfor S2
fa: S3for S4: First Turn Trajectzy--: }:rajectry Generated
by aS teering Magnet: SteeredFiist Tum Trajectry

II8x:Defocusing andFoeusing Quadrupoles: Steering Magnet: MmitorFig. 2 FfS correction sequence

2.2 Rough orbit correction package
With the RF system turned off, the beams are lost
within a few tens turns. Even in this case, the COD can beroughly estimated by averaging trajectories and can becorrected. For averaging, trajectories up to 128th turn can beused at most. The best corrector method [6], so called
MICADO, is used to estimate the strength of steering
magnets.
It should, be noted that the orbit in dispersive sections
shifts turn by turn owing to the radiation loss. The roughorbit correction (ROC) package therefore provides a functionto correct this drift in trajectory data assuming that theenergy loss per turn is constant and that the dispersion islinearly dependent on the energy shift of circulating beams.
The ROC package provides following functions besides
the above dispersion correction: (1) Both the COD after thecorrection and orbit distortion generated by a determined setof stee(ing magnets are shown in the same graph together
with the,SOD before the correction. (2) The strength
distribution of a determined set of steering magnets can beshown in a graph. (3) The rms values of the COD before
and after the correction and the maximum strength used in
the correction are displayed. (4) The maximum number ofsteering magnets to be used can be set for both horizontal
and vertical COD corrections.

2.3 COD correction package
Once the beams are stored in the ring, the COD can bemeasured and corrected with usual COD correction methods.
At present, for the global COD correction, the best
corrector method is used to keep the number of steering
magnets small. It is important for the package to beequipped with functions of processing the COD data to
support the correction. Our package provides following
functions in addition to those provided for the ROC package

except for the dispersion correction: (1) Arbitrary set ofmonitors can be masked from the panel and saved as a data
file. (2) Power spectrum of the COD can be calculated up toa thousandth harmonic and shown in a graph. The highharmonics are necessary because of the low emittance optics
where the phases do not advance in the sections with theBPMs but in bending magnets. (J) The COD can be filteredwith arbitrary cut-off frequency less than a thousandthharmonic .
For the local correction, a single bump orbit generated
by four steering magnets is used. This is mainly applied totentatively adjust the orbit at insertion devices for thealignment of photon beam axis. A graphic system isavailable to select proper steering magnets.

2.4 COD data processor
This processor provides two functions. One is theaddition and subtraction of two arbitrary data. Both COD
and trajectory data are usable. The processed data can be
stored in the database and also shown in a graph.
The other is the estimation of dispersion functions. By
using two COD data each of which has the different beamenergy, horizontal and vertical dispersion functions areestimated. Here, as a momentum compaction factor, adesign value is used.
3 Results obtained in Storage Ring BeamCommissioning

At the beginning of beam commissioning of the storage
ring,· the first turn was completed and the beam wasimmediately stored with both sextupoles and RF system
turned on [7]. Owing to this smooth commissioning, theCOD package was mainly used to correct the orbit
distortion. The FfS package was therefore never applied tothe correction during the commissioning period. On theother hand, the ROC package was often used to correct theCOD at the first stage of the commission)ng. This isbecause the COD package initially had some bugs and aquality of COD data was not good. At present, the bugs has
been filxed and the quality of the data has been improved tosome extent.
Figure 3 shows the COD distributions before and after
the correction. The rms values of the horizontal and vertical
COD are respectively 1.7 and 2.4 mm, which have beenreduced down to about 0.2 mm by the correction. Since lotsof fictitious phase jumps are found at the sections where thephase can be regarded as a constant, this saturation seems tocome from a monitor error.
In the correction, so far, coefficient matrices arecalculated with the optical parameters which are slightly
modified from design values to adjust betatron tunes tomeasured ones. Figure 4 shows the comparison between
measured and expected rms values of the COD after thecorrection. A good agreement indicates the validity of thecoefficients mentioned above as the first approximation used
for a commissioning period. We are now developing asystem to consistently estimate the distribution of all
magnetic errors by measuring the response of a real ring. In-462-

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

future, optical parameters will be replaced by ones based onthe measurement.
Figure 5 shows measured horizontal and verticaldispersion after the COD correction. The horizontal
dispersion is well restored by the COD correction and thisdoes not increase effective horizontal emittance at thestraight sections for undulators. However, some correctionof the vertical dispersion could be necessary for achieving aH-V coupling ratio of 1 %.

2.5

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References

1!!1[1] JAERI-RIKEN SPring-8 Project Team, Facility
Design, Part I, Supplement, 1992.
[2] A. Yamashita, private communication.
[3] R. Tanaka, et al., in Proc. of Conf. on Accelerator
and Large Experimental Physics, Chicago, USA, 1995,
pp. 201-208.
[4] L. Farvacque et al., ESRF-SR/LAT-89-15, ESRF,
Grenoble, France, 1989.
[5] R. Nagaoka et al., in Proc. of 7th Symp. Accel. Sci.
Techno!., Osaka, Japan, 1989, pp. 296-298.
[6] B. Autin et al., CERN ISR-MA/73-17, CERN,Geneva, Switzerland, 1973.
[7] H. Ohkuma et al., in these proceedings.

0X

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1015

2025303540

Number of Steering Magnets

Fig. 4 Comparison between measured and expected rms
values of the COD after the correction. The number ofsteering magnets represents the simple sum of thenumber used in each correction step.

Ideal Dispersion Level(A)! 0.3.~~ 0.2~

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Serial Monitor Number

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ii -0.02> -0.03~t1-0.04-0.05 L..J......L-..J-1....1.....1...J...J'-L.I.....1...L...JL...L....I.....L..J--L...L....L...I...J--L...J.....L...o.-'-l..-l-...l300
250502001501000.;I

Serial Monitor Number~-4-6050100150200250300Fig. 5 Dispersion measured after the COD correction. The
upper right symbols (A) and (B) denote respectively ahorizontal and a vertical planes.

Serial Monitor Number

Fig. 3 COD before and after the correction. The upper rightsymbols (A) and (B) denote respectively a horizontaland a vertical planes.

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