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

FLOOR LEVEL MOTION OBSERVED IN THE KEKB TUNNEL
M.Masuzawa, R.Sugahara, KEK, Tsukuba, 305-0801, Japan
Abstract
The level of the KEKB tunnel floor has been monitored
using tilt meters. A clear diurnal effect, which seems tohave a strong correlation with the outside air temperature,
has been seen. The tunnel level appears to be affected byatmosphericpressure
aswell.
Simultaneous
measurements in the basement floor and at four locations
along the beam line were carried out. They show that theamplitude of the daily floor motion is largest on thebasement floor of the experimental buildings and isreduced on the far side of the expansion joint away fromthe building. Measurement results are shown.

cloudy days. It should be noted that the luminosity
changes as a result of various machine tuning parameters,
and it is difficult to compare the hour-to-hour machine
performance. Daily luminosity does seem to have acorrelation with the temperature.

MEASUREMENT DURING BEAM
OPERATIONKEKB is a two-ring collider with a circumference of3016 m [1]. The tunnel lies about 11 m below the groundsurface. There are four experimental buildings called
TSUKUBA, OHO, FUJI and NIKKO (see Fig. 1). The 8
GeV electron ring (HER) and 3.5 GeV positron ring(LER) intersect at one interaction point (IP) inTSUKUBA.

Figure 2: Machine performance for three days at the endof June.
Fig. 3 shows the floor motion for the same three-day
period as in Fig. 2 The tilt meters were placed on thebasement floor, on the left and right sides of the IP and on
the BELLE detector [2] supports. The tilt meters wereoriented with the x-axis pointing radially outwards fromthe ring, with the y-axis pointing along the beam-pipe andthe z-axis pointing vertically upwards. An upward tilt ofthe outer edge of the ring registers as a positive ∆x.

Figure 1: KEKB tunnel

Figure 3: Floor tilt in x-direction at TSUKUBA
experimental hall.

Tilt meters (Leica NIVEL 20, digital output) wereplaced on the basement floor of the TSUKUBA
experimental hall during the last 10 days of beam
operation before the 2003 summer shut down. The floor
level monitoring was undertaken in order to understandthe day and night effect of the machine performance.
Temperature was measured in three locations: the top of
the TSUKUBA building roof, the ceiling of theTSUKUBA utility space, and the outside.
Thesetemperatures are plotted along with the luminosity in Fig.
2. The first two days were sunny and the roof temperaturerose to 60 degrees Celsius. Luminosity tends to degrade
more significantly on sunny and warm days than on

The tilt data were recorded every 60 seconds. The onehour averages and their standard deviations are plotted. Adiurnal effect is seen in the floor motion, with a peak topeak amplitude of several micro radians. The outside of
the KEKB tunnel starts rising around 4 pm and starts
sinking around 4 am. A longer-term motion is discussed
later in this paper. There were no large differences in thefloor motion among the three locations. The IP floor levelshows a clear day and night effect though it is difficult to
explain the luminosity degradation by the floor motion
quantitatively. The diurnal effect in floor motion might
explain the diurnal effect in the circumference of theKEKB tunnel described in a previous paper [3].

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

TUNNEL MOTION NEAR THE IP
DURING THE SUMMER SHUTDOWN
More extensive floor motion monitoring was performed
during the machine shutdown. The NIVEL 20 tilt meters
were removed from the basement floor of the TSUKUBA
building and placed in the right-side straight section of thetunnel. The locations of the tilt meters are indicated in Fig.
4. The definition of the xyz axes is the same as previously
described.

detector. Its location is indicated as #L in Fig.4. Thebasement floor data and the tunnel floor data aresummarized in Fig. 7. The outside air temperature during
the same period is shown in Fig. 8 along with the IP floor
motion. Again the outside of the KEKB ring sinks in theafternoon and the amount of sinking has a correlation
with the temperature maximum-minimum difference ofthat day. The amplitude of the daily floor motion islargest in the TSUKUBA basement and is reduced on thefar side of the expansion joint.

Figure 4: The tilt meter location in the tunnel. The tilt
meters were spaced at 10 m intervals.
Fig. 5 shows the floor and tunnel level motion
measured in August. A clear diurnal effect is seen. Theeffect in the x-direction is larger than that in the ydirection. The diurnal amplitude is larger for locations #1
and #2. Monitor #4 no longer presents a clear diurnaleffect. The other interesting phenomenon seen is thecorrelation between the atmospheric pressure and thetunnel tilt. The outside of the tunnel started rising on
Aug.9th when a strong Typhoon 10 moved across Japan.
The temperature and the atmospheric pressure are plottedin Fig. 6. The tunnel level appears to be affected not
only by the temperature but also by the atmosphericpressure.

Figure 7: TSUKUBA building and tunnel motion for 10
days. Monitor #3 data had some problem and are notshown.

Figure 8: Outside air temperature and the IP floor motion.
A strong correlation with the temperature is seen withsome time lag.
Figure 5: Tunnel floor motion in the x (left) and y (right)
directions. The offsets in the tunnel level are subtracted inorder to show all data on the same plots.

Figure 6: Outside temperature and atmospheric pressure.
An additional tilt meter (Applied Geomechanics inc.,analog output) was placed on the left side of the Belle

FLOOR LEVEL MONITOR AT NIKKOSTRAIGHT SECTION
The tilt meters were moved from TSUKUBA to theright side of the NIKKO experimental hall. The tilt meters
were placed in the same way as in the TSUKUBA
straight section. A diurnal effect is seen again as shownin Fig. 9. The tilt meter placed closer to NIKKO
experimental hall, presents the clearest effect. Theamplitude is on the order of several micron radians. Thisis similar to what has been seen at the TSUKUBA
straight section. The damping of the amplitude across theexpansion joint is somewhat smaller than in theTSUKUBA tunnel during this period. The outer side ofthe KEKB tunnel sinks in the afternoon as in theTSUKUBA tunnel.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003.
Figure 9: Tunnel floor motion observed at the NIKKO
straight section.

LONG TERM MOTION
Longer term data are presented in this section. Thefloor level has been monitored by the tilt meter placed on
the TSUKUBA basement floor (#L in Fig.4). Fig. 10shows the floor motion in the x and y directions over amonth. A diurnal effect appears in both directions, though
the amplitude in the y-direction is several times smaller
than that in the x-direction (see Fig. 11). There seems to
be a longer-term (several-day) motion in both directions
as well, which might be caused by changes in theatmospheric pressure system. The floor level has beentilting up in the past month. The reason for this is notclear at this point. The level changed rather abruptly inthe last few days in the plot, which might be due to thefact the temperature went down during that period.

Figure 11: Fourier analysis of the floor tilt. The thicker
line indicates the floor motion in the y direction. The
diurnal component is clearly seen in both the x and ydirections.

SUMMARY
The floor motion has been monitored in two straightsections of the KEKB tunnel. A diurnal effect has been
seen during the beam operation and during the summer
shutdown as well at TSUKUBA. The measurement atNIKKO showed a similar diurnal floor motion. The floorlevel has a strong correlation with the outside airtemperature, with some time lag between the two. Thefloor level is also affected by the atmospheric pressure.
These characteristics are very similar to what we saw inthe circumference deviation [3]. The tunnel floor levelmotion is damped across the expansion joint, whichindicates that the source of the diurnal motion is theexperimental buildings. The floor level seems to have along term component as well. This might be coming fromthe seasonal temperature drift. A longer term monitoringof the floor level is needed. The floor tilt may be
implicated in the diurnal effect in luminosity.

REFERENCES

Figure 10: Longer term floor motion. The daily floor
motion is smaller in the y-direction (thick line).

[1] KEKB B-Factory Design Report, KEK Report 957(1885)[2] THE BELLE DETECTOR, NIM A479(2002) p117.
[3] M.Masuzawa,et.al.,“CIRCUMFERENCE
VARIATIONSOBSERVEDATKEKB,”
Proceedings of IWAA 2002, November, 2002.