The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

POSITION OBSERVATION FOR MAGNET UNIT AT SPRING-8
C. Zhang, S. Matsui
JASRI/SPring-8, Mikazuki Kouto 1-1-1, Sayo-gun, Hyogo 679-5198, Japan
Abstract
The position observations for the magnet unit of theSPring-8 storage ring are executed using the laser tracker
for horizontal plane and the precision level N3 or DiNi11for vertical plane. And, the measurements are carried oneach year during the summer maintenance periods tomonitor the changes. This paper will give a briefdescription of the survey methods as well as the results ofmeasurements.

Zeiss DiNi11 (std: 0.3mm/1km) for level survey. In themeasurement the instrument is set in the middle of two
measuring points and measure the height difference
between them. To reduce measurement error the height
difference is measured not only for adjacent points but
also for the points leaped over two points. Total
observations for height differences are 384 in the storage
ring. Fig.1 is the survey network for the levels of themagnet units.

INTRODUCTION
The SPring-8 storage ring, with a circumference of 1.5
kilometres, is constructed mainly on hard rock or partly
on artificial rock to ensure stable operation. The ring isChasman-Green lattice of 48 cells. Each cell consists of
two bending magnets and three magnet units, named a, b,c girder, which load seventeen multipoles. The positionsof magnet units are measured each year during thesummer maintenance periods to monitor their changes.

METHODS OF SURVEYINGThe storage ring tunnel is built surrounding the hill ofMihara-kuriyama. After tunnel construction the survey iscompletely isolated from outside. There is no absolutedatum point (reference point) in the storage ring. Both ofsurveys for the horizontal and the vertical are relative
measurements.
There are two fiducial points on one magnet unit at thetwo ends. Totals of 288 points at intervals of 5 meters
averagely in the storage ring. Both the horizontal and thevertical surveys are measuring the positions of thesefiducial points.
Nowadays the laser tracker (LT) is widely used in
metrology and accelerator alignment. Since the beginningof 1994 we have being used the LT of Smart 310 for
survey and magnet alignment [1][2]. The systemmeasures distance with a laser interferometer, and thehorizontal and vertical angles with two encoders.
According to our experiments, the distance resolution isabout 1.3µm. But the angular measurement is relatively
inferior and around 2 arc seconds at our working
environment. Therefore, the surveys are divided into thehorizontal and the vertical, using the LT and precisionlevel respectively.

Surveying for the vertical
Before 1999 the heights of magnet units were surveyedwith Wild N3 (standard deviation (std): 0.2mm/1km).
Because it is an optical instrument the surveyor usually
feel tired from too much observations. And, themeasurement result is more or less depends on people’seyes. Since 2000 we have being used the digital level

Std. (Between units): 0.02mm
Error rms (For 1.5km ring): 0.2mm
Fig.1 Survey for the levels of the magnet units.

Surveying for the horizontal
In addition to the fiducial points on the girders theobservation for the positions of magnets in the horizontal
needs some auxiliary points on the wall. Unlike thevertical, which has equipotential surface, the survey in thehorizontal has no absolute reference datum. Therefore thesurvey accuracy depends on the survey method and thenetwork.
The survey network, as shown in Fig.2, is basicallycomposed of distance measurements between the targets.
The LT is set station by station continuously along thering. Averagely the LT measures 8 or 9 points from onestation. After one set of measurement the LT is moved
forward by about 7.5 meters and made another set ofmeasurement.

Line: distance measurement; Circle:station of LT set up.
Std. (Between units): 0.05mm
Error rms (For 1.5km ring): 0.5mm
Fig.2 Scheme of survey network for the horizontal.
As mentioned above the LT gives three independent
elements of a distance and two angles. To take advantageof the LT, we usually make use of ‘direct-distance’ as
many as possible because of the inaccuracy of the angle
measurement. The direct-distance means the distancefrom the mirror of the LT to the targets, which is

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

1wgt_96.4
wgt_97.2
wgt_00.7
wgt_02.8
wgt_03.8

0.5dY (mm)measured by the interferometer. On the other hand theindirect-distance means the distance deduced from thecoordinates of points. When measure indirect-distance theLT should be set as near as possible to the extension lineof the two measuring points to reduce the influence ofLT’s angular errors. Presently, we usually adopt the“Direct distance measurement method”, which was first
employed in the alignment of the NewSUBARU ring [3].
In such case, we use only direct-distances [Fig.3] tosurvey and determine magnet positions. The distances areneeded to project onto the measuring plane of thehorizontal when calculating point positions.
The positions of measurement points are resolved withthe adjustment computation method of least squares.

0c14-23-0.5

Underpassrf pitrf pitrf pitc30-36SSBT

Tunnel junctions-1

c04c2 c08c2

c12c2 c16c2 c20c2 c24c2

c28c2 c32c2 c36c2 c40c2

c44c2 c48c2

Magnet Unit

Fig.5 Displacements of magnet units for the vertical.
The consistence of magnet levels is still in ±1mm
according to recent measurement. Some areas that havespecial underground structures show apparently largechanges. Table 1 lists the level variations for some typicalareas and the probable reasons.
Table 1: Level variations for some typical areas.

Fig.3 Direct-distance measurement method in survey

RESULTS OF POSITION OBSERVATION
Since the construction of the storage ring the positionsof magnet units are surveyed regularly to monitor theirchanges. Fig.4 is the survey results for the levels. Because
the measurement is unavoidably has errors and there is nodatum point the ring, to make a comparison between
surveys we fit the data to smoothing curves of locallyweighted least squares. Consequently the displacementsof magnet units in levels are shown in Fig.5.
1st (96.4-5)
2nd (96.9-10)
3rd (1997.2)
4th (1997.7)
6th (1999.8)
7th (2000.7)
8th (2001.8)
9th (2002.8)
10th (2003.8)

1dY (mm)

0.5

0-0.5

-1-1.5
c04c2

c08c2

c12c2 c16c2

c20c2

c24c2 c28c2

c32c2 c36c2

c40c2 c44c2

c48c2

Magnet Unit

C2 indicates the second point on the c girder.
Fig.4 Survey results for the levels of magnet units.

Cell No.

Change amountUnderground struct.

C1,3,13,25,37-0.5 mm

RF pitC9-0.4 mm

Underpass

C36-0.8 mm

Boundary ofconstruction zones

C43-0.3 mm

SSBT transport line

C30-36-0.5 mm

Artificial rockC14-23+0.4~0.8 mm

Soil-removed area

Generally, There are subsidence in the places where
have underground pits, so are the areas that ground wasimproved with artificial rock when constructing the tunnel.
Moreover, some of the areas that were constructed on
hard rocks are observed on upward trend. That iscomprehensible for the area between cell14 and cell23
where the hill was removed and the rock was cut to thesame altitude as others when building the tunnel. It isconsidered that reduce of the mass causes geographic
surface increase. Comparatively, the area of cell 37 – 43,
where is also built on hard rock, has no the trend of
surface rise.
For the horizontal the survey results are showed in
Fig.6. Maximum displacement in horizontal transverse isstill in ±1.5mm after many years. To make a comparison
between measurements the data are removed for low
frequency components by locally weighted fitting and are
showed in Fig.7. It is need to say that the measurements atfour long straight sections (cell6, 18, 30, 42) have large
error because of the change in survey network after thelong straight sections were introduced in 2000.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

21.5

1dX (mm)

0.5

0-0.5
dr_2003
dr_2001
dr_1999
dr_1998
dr_1997(ref)-1-1.5
c04c2

c08c2

c12c2

c16c2

c20c2

c24c2

c28c2

c32c2

c36c2

c40c2

c44c2

c48c2

Magnet UnitFig.6 Survey results for the horizontal of magnet units.
1LSS
0.5

LSSLSSLSSCONCLUSION

dX (mm)0-0.5

SSBT-1

wgt_2003
wgt_2001
wgt_1999
wgt_1998
wgt_1997

Zone boundary-1.5
c04c2 c08c2 c12c2

c16c2 c20c2 c24c2 c28c2 c32c2

c36c2 c40c2 c44c2 c48c2

Magnet Unit

Fig.7 Displacements of magnet units for the horizontaltransverse.
Globally there are no tremendous position changes forthe horizontal transverse since 1997. By comparing with
fig.5 one can see that most of the displacement peaks inthe horizontal are in correspondence with that of thevertical. That is, the displacements are mainly due toground movements and related to the monument positions.
Those monuments were built under the bending magnets
and were surveyed in 1993 before the construction of thetunnel [4]. They were buried into the tunnel groundafterward and used as position references in 1995 in theprocess of magnet alignment. There is a possibility thatthe positions of these monuments had been changed from1993 through 1995 when building the tunnel. Thesechanges should be in a same tendency as that of the levels.
If we examine the relative displacement between
magnet units, Fig.8 gives the results in 1997, 2001 and2003.
0.8(2003) std: 0.10 mm

SSBT
rf pitrf pit

0.2

0.6

00.4

rf pit-0.2

0.2
Zone boundary-0.40(1997) std: 0.05 mm

-0.6
c04c2

c11c2

Relative displacement (mm)1997

Relative displacement (mm)2001, 2003

0.4(2001) std: 0.09 mm

c15c2

c22c2

c26c2

c33c2

The standard deviation between girders has increased
from 0.05 mm rms in the beginning of 1997 to 0.10 mm
rms at present. However, there was little change in past
two years. For the displacements, some particular places(rf pit, SSBT, zone boundary) still can be seen for thelarge variations. Another result is that the displacements
are in short periods with similar pattern. And, thedeterioration of the girder C is mainly toward outside of
the ring. This phenomenon may be related to the vacuum
farce, which is caused by different areas at the two endsof bellows. The force is about 0.8 ton and executes onto
the girders through the fixtures between chamber andgirder and made the girder twisted and moved. We aredoing further investigation about this matter.

c37c2

c44c2

-0.2
c48c2

Magnet unit

Fig.8 Relative displacements between magnet units inhorizontal transverse.

The position observations for the magnet unit of theSPring-8 storage ring are executed using the laser tracker
for horizontal plane and the precision level N3 or DiNi11
for vertical plane. The standard deviations of them are
0.2mm and 0.5mm respectively.
Maximum displacements are within ±1.5mm for thehorizontal transverse and ±1mm for the levels althoughmany years have passed. Some areas that have special
underground structures show apparently changes.
Generally, There are subsidence in the places where haveunderground pits, so are the areas that ground was
improved with artificial rock in constructing the tunnel.
Moreover, some areas that were constructed on hard rocks
are observed on upward trend. For the relative
displacement between magnet units, standard deviation
has increased from 0.05 mm rms to 0.10 mm rms.
However, there were little changes in past two years
according to resent observation.

ACKNOWLEDGMENT
The authors would like to present their thank to themember of SES (SPring-8 Service Co. Ltd) for their workin the measurements.

REFERENCES[1] S.Matsui, C.Zhang, Proceedings of IWAA95, KEK,
Japan,1995.http://www.slac.stanford.edu/grp/met/TO
C_S/1995conf.htm.
[2] C.Zhang, S.Matsui, Proceedings of IWAA95, KEK,
Japan, 1995.
[3] C.Zhang, S.Matsui et al., Proceedings of IWAA99,
ESRF,France,1999.http://www.esrf.fr/conferences/pr
oceedings/IWAA99/index.html.
[4] S.Matsui, I.Takeshita et al., Proceedings of 9thsymposium on accelerator sci. and tech., KEK, 1993.