JAERI-Conf 95-021

PA26
Magnet Alignment System of the SPring-S Storage Ring using Laser
Sakuo MATSUI, Chao ZHANG, and Jun-ichi OHNISHI
SPring-8, Akoh-gun, Hyogo-ken 678-12, Japanand'Yutaka CHIDA
Hitachi, Ltd. Hitachi Works., Hitachi-shi, lbaraki-ken 317, JapanAbstract
The SPring-S storage ring is under construction.
The girders on which several magnets are put are
surveyed with a laser tracker by making network. Afterthe smoothing the relative displacements are within±0.04 mm. A laser and a CCD earner system is used fora precise align?tent of quadrupole and sextupole
magnets on a grrder. The target shift from the 5mstraight line can be measured to be less tban 10 J.UD.
The misalignment of them are estimated to be less than
the torelance.

Introduction
The storage ring has a 1436m circumference whichsurrounds the hill called Mihara-Kuriyama, and has 4S
cells. Each cell has 17 quadrupole and sextupole
magnets put on three girders, and two bending magnets.
Whole ring was surveyed before building
construction two times. After tunnel construction, allmonuments were surveyed again. According to thesesurvey results, the 8S monuments positions weredecided. After the girders are set up, both the end
magnets on the girder are surveyed by the laser tracker
SMART310, and then girders are smoothed.
Five or seven magnets on the girder are aligned~recisely using a laser and CCD camera system andtlltmeters. The hole center on the magnet fiducial plane
are shifted from the line right above the magnetic axis,
and the shifted values have been acquired at the magnet
measurment process. Spherical targets which diameteris 75 mm are used at several steps, that is survey, levelmeasurement, pre-alignment and precise alignment.

Tolerances for magnet misalignment
The tolerances for the magnets of this storage ring
Table 1 Torerances for magnet misalignment~z

rms rotation error•2)ex
6yez(mrad)

nns displacement error• I)
Magnet~X~y(mm)
0.5

0.5

0.5

1.0

1.0

0.1

•total

0.05
0.2
0.21

0.05
0.2
0.21

0.5

1.0

1.0

0.2

Sextupole•magnet

0.05

0.05

•girder

0.2

0.2•total

0.21

0.21

0.5

1.0

1.0

0.5

DipoleQuadrupole•magnet•girder

are listed in Table 1. In order to reduce the sensitivity
to the misalignment of quadrupoles adopted alignment
method is to divide the alignment into two stages, thatis in a girder (torelance 50 J.UD) and between girders(0.2mm).

Monuments Survey 1
Before building construction, 21 concrete blocks
shaped like tombstones were made along the ring every
60 m, and monument plates were buried on the top.
Monument is placed at the intersection point of thestraight lines at both sides of the bending magnet.
These monuments and geodetic points outside the ringwere surveyed two times with a distance meter ME5000
and a theodolite T3000. The error ellipses of theseresults were smaller than the circle of radius 1 mm.

Monuments Survey 2
The laser tracker is for the first time employed in
the measurement of storage ring networks.
The SMART is a dynamic
measurement system, thatis laser can chase the target
wherever we move. Thissystem consists of a laserinterferometer, a rotating
mirror on two axes with
two angle encoders andservo motors, a position
diode etc. The tracker gives
3D spherical coordinates ofa target in space with adistance resolution ofFig.1 Principle of the1 IJ.m, an angularlaser tracker
resolution of about 1
arc sec..
Experiments show the laser tracker has a distanceaccuracy of 0.001+0.2ppmXL(mm) and an angularaccuracy of 10 IJ.rad. This accuracy will result at least
7.3 mm traverse disclosure for the storage ring orbit if
SMART is simply used for coordinate measurement.
Alignment network for SPring-S storage ring isdesigned as a distance-only trilateral network. Several
aspects are optimized. The laser tracker has differentaccuracy for distance measurement when its positionchanges in respect to measuring targets. To reduce theinfluence of angular error, the laser tracker's positions
within network are chosen by checking the distanceaccuracy it results:
MF*1)~. ~y. and~ denote the horizontal, vertical, and longitudinal

displacement errors, respectively.
*2)6x, 6y, and ez denote the rotation errors around the horizontal,venical, and longitudinal axes, respectively.

(li-lzcosa)2 2-(lz-llcosa)2 2~(111zsina)2. 2
Im,l "f\Im,2 p2
Inlu

where 1 is the length between two measuring points,
a, It, 12 are angle and lengths from laser tracker to-97-JAERI-Conf 95-021

these points, ma, m11, m12 are their measurement
accuracy respectively. To calibrate measuring distance,
a 20m-long stand is being made to compare SMART
with HP 5527A interferometer.
When putting the target on the monument, atripod is used. The laser light when measuring the target
is in the plane which height is 1700mm. The height ofthe stage on the wall is also 1700mm. The body of
SMART sensor unit is modifyed so that we can adjust
the height and shift horizontally. This is because thesurvey can be carried out without using the rotary
encoder for vertical angle.
After tunnel construction, all 88 monuments
including 21 points were surveyed with SMART.
Since this survey network w·as narrow and thecircumstances were not good, it was difficult to decide
the monuments coordinates using only SMART. Thus
the data of the ~gles between the 24 monuments wereadded. The difference between survey1 and survey 2 wassmall.

Magnets Setting
The quadrupole and sextuole magnets are set.

14 nnwmmnwwmmwn~mnnwmmmw~~
12 .............,.................

10 ..........................

4 J-............. ,200.70 0.76 0.81 0.87 0.93 0.99 1.041.10
Maximum Displacement (mm)Fig.2. Maximum magnet displacement of twenty
time simulations.
3. Survey
After repeating this 1-2 cycle two times, survey ismade. If this result is good, girder alignment is finished.
Primary magnet installation results show that therelative displacement between girders of ±0.04 mm has
been achived.

Alignment of both end magnets on the girderThere is a fixed target stage on both end magnet.
This stage is used for the alignment between girder§ andfor a reference stage of the precise one in a girder.
Both the end magnets are aligned using survey2results. This alignment is necessary before girderalignment. The magnets except both end .are alsoaligned roughly to make shorter the time used for
precise alignment in a girder.
Alignment between girders
1. Survey
The network precision depends on both the accuracyof laser tracker and the structure of network, and also theratio of measurement length to the width of net.
Measurement lengths are optimized by simulation studyof error accumulation. The results show that themeasurement length shorter than 15 m (1/2 cell) has
least error accumulation rate along the ring.
The alignment network is composed of 288
quadrupole fiducial points and 96 auxiliary brackets on
inner wall. Over 50 percent distances are measured
directly by laser tracker interferometer. Precision formagnet positioning is estimated on the assumption thatthe distance measurement errors have a Gaussian
distribution. Error ellipse analysis shows thatmaximum position displacement of magnets in respect
to geodetic coordinate less than ±1 mm, relative
displacement between adjacent girders of ±0.05 mm areexpected. Simulations results are well coincide withprecision estimation.
First survey and smoothing is 4 cells, second 8cells, third 8 cells, .. and so on. Also the monuments aresurveyed for references in these survey. The shift values
from the smoothed fitting curve are calculated.

E'E

0.4
0.2·---~·+····--··!········{·········}········!········+········}-- .. ···5E 0.0~-·rlr#rtq,;:o'ii'fb&>~~-0·'I::'ClI0l0l ~c9 !

l 0······f········l········t·······f.:... j....~···.0.2. . . t. . . . ,. . . .+. . ·+·"""1···:§:3. ·.0.4

j""'" .0.6

lttP l050

100 150 200

250 300 350

400

Dirtllnce(m)Fig. 3. Relative displacement between girders.

Level survey
The level reference on the wall is for pre-alignmentof the magnet. It is important to smooth not the wallreferences but the magnet stage. This level survey isdone after the girder position on the horizontal plane is
fixed and is locked. Wild N3 is used. Now NA2 with adiode laser instead of N3 is tested. A PSD(PositionSensitive Devise) is used as the detector. However, thismethod is too sensitive to the NA2-PSD distance.

2. Smoothing
The girders are adjusted according to these values.
The girder is monitored with eight digimatic ingicators.

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Alignment of bending magnet
Bending magnet is aligned with SMART after theFig.4. Tiltmeter and SMART target on it.

JAERI-Conf 95-021

spacial filter
ND filter

pinholecollimator~~~~~~~~~~~-

hood with diaphragmstages for fine adjust::!

Fig.5.

Fig.7. Stage on which thetaget is put.

;

Laser with spacial filter and collimator.

girder alignment. Target for SMART is put on thetiltmeter as shownin Fig. 4. and its coordinates are
displayed in real time on the CRT.
Alignment of quadrupole and sextupole
magnets in a girder-- Laser and CCD camera System -A laser source is put on the fiducial plane of thealigned bending magnet because the adjust of laser iseasy. This He-Ne laser shown in Fig.5. has a spacialfilter and a collimator to make parallel light beam ofgaussian shape. The diameter of a pinhole is 25 ~·The diameter of the light beam is about 3mm and itschange is within 2% from 1m to 5 m. A CCD camera
is used for a detector shown in Fig.6. The CCD camera
can always see the distribution of light beam which issensitive to the mechnical stress because of small
pinhole.
ND filter 1/100

Fig.6. CCD camera with spherical housing.
It is difficult to receive the laser light directly on theCCD device because of the interference striped pattern.
Thus the coating to suppress the reflection is used.
However the interference pattern remains a little. TheCCD device on which an optical fiber plate was tested.
This camera showed no interference pattern, but it was
too sensitive to the incident angle of the light.
The signal of the image comes into a video frame
grabber board in the Macintosh computer. The center
coordinates are extracted from this two dimensional
distribution. Thouth the size of a CCD cell is 11 ).tm x11 ).tm, the accuracy of this system is about ±2 ).tm inthe ±0.5 mm region at 60 em distance. The total
counts of summed up distribution is of the order of 108·
The straightness of this laser and CCD system waschecked with 4m-long stage. The small deformation of
the stage was observed by a tilt sensor. The straightness
is estimsted to be within 10 ).tm during 4m. If there isno pinhole in the filter, the straightness became bad.
It is important to place the camera in the housing sothat the center coordinates do not change even if thespherical housing rolls a little.
The hood is quite important to stop the air flow.
The magnets on the girder are usually aligned where thewind velocity is around 0.02m/s.
The change in temperature is very small in thetunnel. Thus the direction of laser beam is rather stable.
The drift of laser beam observed at the distance 6m is
usually within 10 ).tm during a few hours.
One or two planes are made on the magnet for thefiducial ones, and has a hole into which the stage isinserted. The diameter of this hole is 20 mm and its
fluctuation among the fiducial planes was over_20 ).tm.
Thus the ball cage is used as shown in Fig.7. It is easy
to take the stage in and out the hole.
The reference line used for alignment is 0.5 m upper
than the electron beam axis, thus the roll of the magnet
is very important. It is difficult to measure the tilt
precisely with a tiltmeter if the span between thecontact points is short. A means to get good
repeatability is necessary.
Since the tolerance between the girder is lager thanthat of magnets on one girder, firstly, both the end
magnets are aligned. The fixed target stage is adjusted
only the height, because this position is already aligned.
While the magnet is being adjusted, not only CCD
camera but also 8 digimatic ingicators are used tomonitor the magnet shift. The shifted values are
displayed on the CRT also. Operators adjust themagnet looking at the ingicators. These ingicators areuseful for moving to an accuracy of several ).tm.
The adjust of each magnet continues until thedisplacement at the position of CCD camera becomes
within 10 ).tm on the CRT monitor.
Acknowlegements
We would like to thank Dr. K. Endo, Dr. R.
Sugahara, and the personnel of KEK survey alignment
group for their useful advice and Dr.A.Ando fordiscussion. We are much indebted to the staff of ourmagnet group and also acknowledge to Mr.
M.Kawakami, Mr. K. Nakashima, Mr.I.Takeshita andcollaborators of Hitachi Plant Engineering &Construction Co., Ltd. for their help.

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