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

Floor Level Fluctuation in Accelerator Tunnel
Masashi J.SHIRAKATA, Hikaru SATO, Katsumi MARUTSUKA
and Noboru TOKUDAHigh Energy Accelerator Research Organization,
1-1 Oho Tsukuba Ibaraki 305, JAPAN1. Introdluction
Magnet alignment is one of the most important factor
for stable particle aceleration. In the KEK-PS main ring,the magnets are aligned in 100 Jlm. In . 1996 fall, thema~net realignment was done in order to expand theverttcal acceptance during the beam injection . period.
Since the main ring was constructed, a continuous
degradation of the floor has been observed for about 20years. The floor subsidence was mostly brought about by
the radiation shields located in the experimental hall. In
fact, when the north experimental hall was constructed,
the. large subsidence of the floor around the beam
extraction area was observed[!]. The most origin of thecontinuous floor subsidence is the heavy materials for theradiation shields, and even now the floor is moving very
slowly.
The floor subsidence accompanies the corresponding
floor upheaval in opposit side of the main ring. As aresult, the main ring tunnel inclines and the difference
between lowest and highest points has exceeded 2 mm.
This floor level fluctuation was considered as ratherslow phenomenon in the order of years. In these days, theproblem with the floor level fluctuation is closed up since
the fast floor movement was observed. The floor level
fluctuation damages on the precise magnet alignment andcauses the reduction of aperture. It is conjectured that thefast floor fluctuation comes from the moisture in the soil.
2. Observed Floor Level Fluctuation
Although the magnet realignment works were carriedout several times, they ended the correction only for thelargely deviated magnets and the correspondency with thebooster ring was not considered. The systematic magnet
realignment was needed in order to achive the higher
beam intensity in the main ring.
In the summer shutdown period of 1996, magnet
alignment was carried out from September 2 to 13[2].
Figure 1 shows the height of 56 quadrupole magnets
before and after the alignment. The first measurement
corresponds to the before alignment and the others areafter alignment. The zero level corresponds to the heightof the exit of the booster ring. As shown in it, the MR
tunnel is inclined and have some bumps. Roughly seeing,'the injection area subsided and the opposite area raisedaround the booster extraction height as the center.
Especially, quadrupole magnets No.1 to 16 and No.53 to
56 were located in very low level. At first, No.3 to 16
were tried to be adjusted to the level of No.2, which wasoften refered as I-ID and was the first quadrupole
magnet for the injected beam.
In this work, a significant unconformity of themagnet height which became about 1 mm was observedby the second height measurement. The height of the-516-

1.0

I o.o~"Q)::c: -1.0
-2.0

56.0

Quadrupole magnet number
Figure 1. Height of Quadrupole magnets
Height zero corresponds to the heightof the exit of the booster synchrotron
quadrupole magnet differed after a round trip. It must be
notified that the quadrupole magnets No.3 to 9 havealready been adjusted to the No.2 (called l-ID) by thealignment work. In the first height measurement, magnet
No.3 to 10 were apparently located lower with respect tothe No.2. After the weekend these magnets became
higher, especially for No.lO, it became already higher
than No.2, which is the reference magnet.
Though the lattice structure of the KEK-PS
accelerator has a four-time symmetry, the constructionsof the foundation are not. The floor in the main ringtunnel consists of eight separated blocks but they don't
have any symmetry. Around the beam injection area, thefloor is divided into three plates called as C2 , Dl and D2.
The quadrupole magnets No.53 to 56 and No.1 to 3 are onthe plate C3. The No.4 to 8 are on the plate Dl. And theNo.9 to 14 are on the plate D2.
The floor level unconformity shown in Fig. I can be
explained by assuming these conditions:(1) Plate C2 is inclined (downstream end is LOWER)(2) Plate Dl is inclined (downstream end is HIGHER)(3) Plate D2 is raised
It must be considered that the quadrupole magnets
were moved according to the floor plates in order toexplain this unconformity of the magnet height. After thefirst height measurement, there were two days of blank

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

time before beginning the alignment work because of theweekend. There was a heavy rain from the Sunday to theMonday morning after long sunny days. It is supposedthat plenty of water of this rain might move the floor
plates in the main ring tunnel. In the third heightmeasurement, the magnet height can be seen returning to
the first state. The quadrupole magnets around the joint of
the plates C2 and D 1, and those on the plate D2 became
higher compared to the second measurement. It
collaterally supports the assumption that the rain makes
the floor plates move upward and downward.
In November 1996, the beam orbit fluctuation wererecorded with the weather condition[3]. Figure 2 shows
the changes of the vertical COD in the main ring. Thisorbit recording was carried out from Nov. 5 to 25.

40.0
20.0
20thtoNov.l9th

60.0

5. 0 11/1----,---,.-------.-----.-,--....-----I~ O.Oli-.~~~----~~~~~~--~

:g

40.0
20.0
Quadrupole magnet number
Nov.14th to 15th

60.0

1 -----'----llll-5.0 ----'-------'1' ------'-------'-40.0
60.0
20.0
0.0
Nov .20th to 21st

5. 0 11,1------.-------r,--.--..,.,--.------111

-=

0.0

0.0

~I-5.0
0.0

40.0
20.0
Nov. 15th to 18th

60.0

-5.0
0.0

I

5.0

5.0

Nov.22nd to 25th

Nov.l8th to 19th

Figure 2. Orbit excursions in the vertical direction-517-I

40.0
20.0
Nov.2lst to 22nd

60.0

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

Unfortunately, in this period little rain was observed
because it was winter.
The orbit change of about 0.5 mm was observed forthree days of Nov .18th through 20th and four days of
22nd through 25th. These orbit excursions corresponds tothe magnet deviation of about 200 !liD. During themeasuring period, it rained twice on 15th and from 20th
evening to 21st early morning. Soon after the latter
rainfall, the large COD was observed as shown by
Nov.22-25th data in Fig.2. Hence, the floor movements
can be attributed to the rain. However, it is difficult to
explain the correlation between the rainfall on 15th andthe orbit excursion from 18th to 20th, because the amountof precipitation was little, and there was a time lag of four.
days until the orbit excursion appeared.
It is remarkable that the COD can change into theopposite phase. (See Nov.I8-20th and 22-25th data inFig.2.) It means the error souce of the COD changed thepolarity. Although the fluctuation on the power supply
makes the COD, it cannot change the polarity. Theassumption of floor plate movements well explain suchcharacteristics.
3. Origin of the floor movement
The KEK-PS was constructed on the water-richground. At first, it was considered that the undergroundwater makes the floor move because there are twomoisture strata below the main ring. According to thewater surface level measurement from the well, any
anomaly was not observed during above period discussed
in section 2[4]. The velocity of water percolation
downward through the soil was found very slow. It
typically takes several days for making some changes
onto the water levels in the moisture strata. This factcannot explain the rather fast (in one or two days) floor
level fluctuation observed in September 1996.
The main ring kmnel was constructed on the ground(not underground!) with the banking. In the case of thistype tunnel, the stress on the constructions mainly comesfrom the moisture which is contained in the banking. In
this mechanism, the fast effect can. be explained. Themoisture measuring system is now under preparation toseize the flow of water in the banking in company withthe Radiation Science Center and the Geological Surveyof Japan. The banking of main ring tunnel is 4.5 andpartly 7.7 meter high over the tunnel roof. Osmometers
are distributed in the banking with 3, 4 and 5 meter deepin the banking. It is expected to become clear the originof the floor movement by comparing with the beam orbit
excursions.
4. Conclusion
It is considered that the floor level fluctuation in themain ring tunnel mainly comes from the water in theground. Firstly, although the underground water became
the main candidate, it might not explain the fast floor
movement because the percolation velocity downward
through the soil was very slow. In the case of the main
ring tunnel which has the banking, moisture in the soil ofthe banking plays an important roll geologically. It is
supposed that the moisture in the banking moves the floor
plates in one or two days.
The · fluctuation with the range of about I mm
observed in the KEK-PS main ring tunnel may cause
serious effects on the beam in a future accelerator to be-518-

constructed in this tunnel.
References[I] K.Marutsuka et al., SR-260, KEK-PS Internal
Report, Oct. 1990
[2] M.J.Shirakata, MR-112, KEK-PS Internal Report,Oct. 1996
[3] M.J.Shirakata, Res. & Inst. Subgroup Memo Vol.OIO,
KEK-PS Internal Report, Oct. 1996
[3] M.J.Shirakata, SR-407, KEK-PS Internal Report,
June 1997[4] H.Sato et al., ASN-372, ~K-PS Internal Report,
Oct. 1996