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

Orbit Collection at SPring-S Synchrotron
Naoyasu HOSODA, Kenji FUKAMI, Tsuyoshi AOKI, Soichiro HAYASHI, Toshiaki KOBAYASHI,Hiromitsu SUZUKI, Norio TANI, Mitsugu TANIMOTO and Hiroto YONEHARA
Accelerator Division, Japan Synchrotron Radiation Research Institute (JASRI),Kamigori, Hyogo, 678-12 JAPAN

Abstract
The commissioning of the SPring-S synchrotron wasstarted in December 1996 [1]. After the acceleration ofthe electron beam to 8 Ge V was confirmed, we measured
the closed orbit distortion (COD) by using with 80 beam
position monitors (BPM). The root mean square (RMS)of the horizontal and vertical COD at 8 GeV are 1.10mm and 2.57 mm respectively. The COD was correctedby the method based on sensitivity matrix (Smatrix).
An Smatrix represents the effect of each correction magnet on each BPM. As the results of correction, the RMSof the horizontal and vertical COD at 8 Ge V decreased
to 0.4 7 mm and 0.38 mm respectively. We also corrected the extraction orbit by the local bump method.
In March 1997, electron beam of 8 GeV was supplied tothe storage ring successfully.

1 Introduction
The synchrotron [2] receives an electron beam of 1
GeV from the linac, accelerates it to 8 GeV and supplies
it to the storage ring with a repetition rate of 1 Hz. The
circumference of the synchrotron ring is 396.12 m.
There are 80 BPMs which have 4 button type electrodes [3]. The BPM is located in front of every
quadrupole magnet. Beam position is estimated fromthe 4 electrode output signals at the synchrotron main
computer [4]. Total measurement time of the 80 BPMs is30 ms. The error of the position measurement including
the calibration and the alignment is 0.3 mm .
There are 40 horizontal correction magnets (CH)and 40 vertical correction magnets (CV). The maximum
excitation current of the correction magnets is 7 A. The
kick angle per 1 A of the magnets are 0.5153 mrad/ A
for CH and 0.3473 mrad/ A for CV except for 0.3351
mrad/ A for CV20. The excitation current and the timeinterval for the injection and the extraction can be set
from the synchrotron computer. The power supplies ofthe correction magnets near the extraction section (fromCH17 to CH20 and from CV17 to CV20) are bipolar
type, so the angle and the direction of the kick can beselected at injection period and extraction period individually. The others are unipolar type. The directionof the kick can not changed in a repetition cycle in thistype.

2 Smatrix
An Smatrix has the elements which represent theeffect of each correction magnet on each BPM [5]. An
Smatrix is defined as(1)1.5 .------,r---.----.----..-----r--- .---...----n
MeasuredDesigned --+-----1-1.5 L-----"'------'----'----'-----L----'- ----'--.......l80706050403020100BPM numberFig. 1 Response function of CVl. Excitation current
is 0.2 A. CV1 is located between BPM1 andBPM2.
where 8Zj is a change in the position at the j-th BPM
and 8K; is a change in the kick angle by the i-th correction magnet. If we could know Smatrix in advance, theexcitation currents to correct the measured COD is estimated by the position data of BPMs and Smatrix. We
treat Smatrix for horizontal and vertical directions independently. The orbit correction by using with Smatrix
is the method without any model. If the reappearanceof the BPMs and correction magnets are good, the correction works effectively.

3 Measurement of Smatrix
After tuning of the ramping pattern of the dipole andthe quadrupole magnets, we confirmed that the beam
was accelerated to 8 GeV and its orbit was reappeared.
In order to correct the COD, Smatrix must be prepared.
We measured three types of the COD data to change theexcitation current for each 80 correction magnet. The
excitation currents of the magnets were selected to 0.2
A, 0 A and -0.2 A respectively to measure the data of theenergy of 1 GeV. The response functions of the each correction magnet are defined to subtract the COD data of0 A setting from the COD data of0.2 A ("0.2 A) setting.
All response functions were checked graphically, becausesome BPMs have poor reappearance. Typical response
function is shown in Figure 1. Design data was calculated by the orbit simulation program code TRACY V[6]. By changing the timing of the data taking of theBPM, the COD data of 1 GeV and of 8 GeV were measured. The excitation currents to measure the data ofthe energy of 8 GeV were selected to 1.6 A, 0 A and -1.6
A respectively. We prepared 4 Smatrices for the case of-499-

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

1.6
Horizontal, 1GeV - + Vertical, 1GeV -~---­
Horizontai,8GeV ··•····
Verticai,8GeV -><···

1.4
1.2

"E"E00(.)

00.8(.)

l9c:0(/):::<a:2.§.

.§.
0508.570 MHz - + 508.575 MHz -~---508.580 MHz ··a····508.585 MHz • ·30.6

20-1-~

J:

0.40.2-2-3-4 [__.___..___ ..___.l.--._... .___....__0203Correction time

450Fig. 2 RMS of horizontal and vertical COD at theenergy of 1 GeV and 8 GeV.

1020304050BPM Number60_.___u7080Fig. 3 Horizontal COD against the different radio frequencies.

Table 1Results .after 5 times COD correction. h:horizontal ,v:vertical, unit:mm

Data •Fit ··-----"E.§.

RMS
1GeV
BeforeAfter
8GeV
BeforeAftermax

0average
hv

hv

hv

1.31
0.58

1.55
0.42

3.69
2.07

3.74
1.58

-0.35
-0.48

-0.04
0.05

1.10
0.47

2.57
0.38

3.26
2.22

5.76
1.40

-0.36
-0.44

-0.03
0.04

0

(.)

l9c:

2-~

..c:

0"'~

~

508.57the horizontal and vertical COD at the energy of 1 GeV
and 8 GeV.

508.575
508.58radio frequency (MHz)508.585

Fig. 4 Average values of horizontal COD against thedifferent radio frequencies.

4 COD correction
To correct the COD, the excitation current of eachcorrection magnets were evaluated by the most effective
corrector method ba8ed on the measured Smatrix. We
iterated COD correction until the effect of the correction was not recognized. Figure 2 shows the RMS of thehorizontal and vertical COD at the energy of 1 Ge V and8 GeV in the COD corrections. The RMS, maximum
values and average values of each case are listed in Table 1.
The average values of horizontal COD is not
negligible small. The reason should be that the circumference of the synchrotron is different from the designvalue. The horizontal COD was measured by changing
the radio frequency as shown in Figure 3. The sections
between BPM35 and BPM41 and between BPM75 andBPM1 are the dispersion free sections, so the horizontal displacemen ts by changing the radio frequency arenegligible small. Figure 4 shows the average values ofhorizontal COD against different radio frequencies. By
fitting these values, the radio frequency that the averagevalue of the horizontal COD becomes zero is 4kHz lower
than the design value of 508.58 MHz. It proves that thecircumferenc e of the synchrotron is 3.1 mm longer thanthe design value. Figure 5 shows the COD with correction and without correction for each case.
5 Local orbit correction
After the COD correction, the electron beam of 8
Ge V was supplied to the synchrotron beam dump. To
correct the vertical position and slant of the extraction
orbit to the center of quadrupole magnets at beam dump
line, the local bump orbit around the extraction section
where 4 septum magnets are installed was made by successive 3 CVs. Figure 6 shows the layout near the extraction section. The position of the extraction orbit
did not have to be adjusted, because already there wasin good position by the COD correction. The slant ofthe extraction orbit was adjusted to be negligible small
by CV20, CV21 and CV22. The vertical COD correctedby the !local bump method at the extraction section isshown in Figure 7. The local bump orbit is seen between BPM41 and BPM43. At the other points except
for poor reappearanc e points of BPM3 and BPM45, thedifference between the CODs with and without correction is not seen.

-500-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

6,----r---.-----.----,------.-- .-----,..--.,.,
Horizonta1,1 GeV

E.s
Cl0(.)

cvi

With correction Without correction -+---

42Extraction LineI
I$eptum

19I
I
III
I
I

0-2-4-6 L--~--~-~-~-~--L--~-~
80
70
60
50
40
30
20
10
020

2221

BPM

BPM Number

6 ,----r---.-----.----,------.--.- ----,..--.,.,
Vertical,1 GeV

Fig. 6 Layout near the extraction section.

4E.sCl0(.)

20With correction Without correction --+-----22-4-6 L--~-~-~--'--~----'L--~-~
80
70
60
50403020100.s

6 .---r---r---r-~-----.-~.-----.--.,.,0

Horizonta1,8GeV.sCl0(.)

Cl(.)

With correction - + Without correction -+---

4EE

BPM Number

0100;:

2>"'-10-2-2Extraction point-4-3 L---'----'----'---~-~-~--'--~

0-6 '----'----'----'----'-----'---- -'--'----'"'
80706050403020100BPM NumberCl0(.)

30405060

7080

Fig. 7 Local bump at the extraction point. Local
bump is made by CV20,CV21 and CV22.

4E20

BPM Number

6.s

1020v~-2-4-601020

304050607080

BPM NumberFig. 5 Horizontal and Vertical COD at the energy of
1 GeV and 8 GeV with correction and withoutcorrection.
6 Conclusion

An Smatrix was measured for the 80 correction magnets and the COD was corrected by these Smatrices.
The extraction orbit was corrected by the local bumpwhich is made by the 3 CVs. An Smatrix-based orbit correction was very effective at commissioning of thesynchrotron.

SPring-8 synchrotron" to be published in Proc. 6th
International Conference on SRI97.
[2] H. Yonehara et al., "Synchrotron of SPring-8",
Proc. Particle Ace. Conf. (1993) 2039.
[3] T. Aoki et al., "Beam position monitor for theSPring-8 synchrotron", Proc. SRI95, Rev. Sci. Instrum. 67 9 (1996) 3367.
[4] N. Tani et al., "Control system for the booster synchrotron of SPring-8" Proc. IWCSMSA96, (1996).
[5] H. Nishimura et al., "Orbit control at the ALS
based on sensitivity matrices" Proc. Particle Ace.
Conf., LBL-36443 (1995).
[6] H. Nishimura , "Accelerator modeling and control
using Delphi on Windows NT", Proc. IWCSMSA96,(1996).

Acknowledgment

We would like to thank Dr. H. Nishimura for hiscomments and suggestions about Smatrix and program
TRACYV.
References[1] H. Suzuki et al., "Beam commissioning of the-501-