DEVELOPMENT OF STABLE SUPPORT STANDS FOR ACCELERATORS
H. Matsumoto, S. Takeda, N. Sato, KEK, Tsukuba, Japan
T. Shintake, H. Kitamura, RIKEN, Harima, Japan
A. Suzuki, H. Yoshioka, TAKENAKA Co., Tokyo, Japan
M. Ohtsuka, N. Yoshimura, OHTSUKA Co., Tsukuba, Japan
Abstract
We have developed a very stable support stand using
high strength concrete, and a very precise mover system
based on a simple roller cam. At 13 weeks, the highstrength concrete has a compressive strength (166N/mm2), which is 4.4 times higher than that ofconventional concrete. The mover has shown ±0.1 µm
absolute position repeatability over a ±1.0 mm region.
We have confirmed that the combination should satisfy
the requirements of the 500-GeV (C.M.) e+e- linear
collider [1] and also those of new accelerators such as theinjector linac for the FEL [2].

1 INTRODUCTION
The Japan Linear Collider (JLC) should have anextremely small emittance (an invariant emittance of 30nm) to secure the required luminosity; thus precisealignment of machine components is essential to preventemittance dilution. In the case of the C-band (5712 MHz)
main linac, the tolerance translates to 50 µm for themaximum bow of a 1.8 m long structure.
The components of each beam line have to bealigned with high accuracy. The standard deviation of any
point over a range of the maximum betatron wavelength
in the vertical direction should be better than 30 µm. To
realize those requirements, the main linac will be built
over a very stable granite bedrock. A precise alignment
system for the accelerator and the Q-magnets has toprovide an accuracy within ±50 µm and ±1 µm
respectively, and yet the method must be simple.
Two very important considerations for the support
stand that are that it be vibration proof and have a low
thermal expansion coefficient in order to provide a
precise and stable support system for the long term. In
fact, most accelerator components such as the rf
structures and Q-magnets have their own major vibration
sources (generated by cooling water flows, etc.). Other
major sources are environmental noises from automobile
traffic and so forth.
The usual steel box type support stand is widely
using for accelerators, because the structure allows great
flexibility and is available at reasonable cost. However,there is no massive structure and the stiffness is not high.
Thus, from the vibrational stiffness point of view, thestand is the weakest link in providing for accuratealignment of the accelerator components. It is well known
that a natural granite standard table is very stable, becauseof its massive structure as well as high compressive
strength. Thus, it has much better qualities for damping
vibrations than a steel stand does. Furthermore, granite’s
thermal expansion coefficient is on the order of 10-6 [/°C],that is almost same as sintered aluminum ceramic, and thelarge heat mass of granite tables dampens changes due tovariations in the ambient temperature. However, it is noteasy to make the various shapes that are required for
different accelerator components. Thus, we decided todevelop a new concrete, which can be fabricated easily
and yet otherwise perform like a natural granite table.
We will use a roller cam type precise position moversystem for the rf structures and the Q-magnets, since thedesign concept for the system is simple and sufficientlyreliable to deploy on a large scale to do remote control
positioning of several thousands of rf structures andQ-magnets [3, 4]. The roller cam differs from theconventional position movers such as the push-pushscrew adjuster, the wedge jack adjuster or kinematic
suspension using multi-spherical joints.
In this paper, we will discuss the details of ourexperimental results on the new high compressive
concrete and simple roller cam type mover system.

2 HIGH COMPRESSIVE CONCRETE
2.1 Concept to Development
In general, various conventional concretes havegood characteristics that can provide a low thermal
expansion coefficient and massive structure. However,
it is well known that they can suffer from slow volumeshrink, slow shape creep and hairline cracking.
Thus, we decided the performance targets for thenew concrete for the support stands to be as follows:
1) Increase the compression strength,2) Small volume shrinking after drying,3) Small creeping deformation of the shape,
4) No hairline cracking as the material ages.
5) No need of any sub frames, such as reinforcing rods.
To achieve the target performance, the concrete
components (by volume percentage) were foundexperimentally. Table 1 shows a comparison of the main
compositions for the resulting high compressive andconventional concrete.
The main components and also their relative
amounts in the new concrete were optimized to obtain avery high compressive strength and a very small
shrinking in volume while still meeting the otherremaining requirements for a stable support. The newconcrete has a liquidity very much higher than that ofconventional concrete. This contributes greatly toincrease the concrete density per unit volume.
Table 1: Comparison of conventional and new concrete.
ITEMS
New concrete Conventional
Ratio of water and cement (%):
2056.1
Content of fine aggregates (%):
5249.3
Content (kg/m3)
171
160- Water:
305
800- Cement:
886
821- Sand:926
671- Pebbles:
Chemical admixtures (kg/m3)
no content
10.4- High-range AE1):
no content
8.0- Highly durable2):
3.05
no content- AE water-reducing3):
1) High-range water-reducing and air-entraining admixture.
2) Highly durable admixture.
3) Air-entraining and water-reducing admixture.

We made four full size support stands; cylinders 500
mm in diameter and 680 mm tall as shown in Fig. 1. After
grinding with a special machine, measurements of the top
showed a surface roughness less than 10 µm on average,
and a flatness of around 10 µm.
To compare the
newly developed andconventional
concretes
we used Japan Industrial
Standards (JIS) for our
appraisal standards. Twofull size samples wereused to measure thecompressive strength andthe volume shrinking as aFigure 1: Sample concrete.
function of the time. To
investigate
thedryshrinking characteristics of the concretes, each samplehad two reference points spaced 300 mm apart marked on
the surface and located parallel to the central axis asshown in Fig 1. The variations in the distance between
marks as a function of the material age were recorded.

Figure 2: Comparison of the compressive strength of the newand conventional concrete as a function of material age. The
new concrete provides 4.4 times higher compressive strengththan conventional concrete at 13 weeks.

Figure 3: Comparison of dry shrinking in the new andconventional concretes as a function of material age. The newconcrete maintains very small dry shrinking at 13 weeks.

natural granite tables for precise support stands.
Fig 4 shows the full size support table (Ø500 mm x680 mm) made from this high compressive concrete. Thesurface roughness and flatness at top are both within ±10µm. An alignment accuracy of ±10 µm was reached inless than 30 minutes of working time. The support standwill be glued onto the base granite using a mortar binder
after alignment. We are now preparing to glue the support
stand in place, and then to make long-term position
stability measurements.

2.2 Experimental Results
We obtained very good experimental results fromthe new concrete. The measured typical compressive
strengths and the dry shrinking of new and conventional
concretes as a function of material ages are shown inFigures 2 and 3.
As can be seen in Fig. 2, at only 13 weeks the newconcrete provides a compressive strength 4.4 times higher
than conventional concrete, note that it is also higher thannatural granite block. Fig. 3 shows that at a material ageof only 13 weeks the variation curve for dry shrinking of
the new concrete is almost saturated at 69 x 10-6. The newconcrete has only 38% of the dry shrinking value
compared with conventional concrete. From this result,
we clearly confirmed that the new concrete could replace

Figure 4: Full size support stand and attaching alignment jig
were developed by Takenaka Co. The surface roughness andflatness are within ±10 µm.

3 ROLLER CAMS MOVER
This mechanism is designed to support a load of up
to 500 kg, while providing smooth motion, free ofhysteresis at the micron level. The new roller cams mover
unit is comprised of two roller cams, their stepping
motors drivers, two linear sliders and support frames. A
conceptual drawing of the roller cams positioning system
is shown in Fig. 5. We used 72 mm diameter roller cams

Figure 7: Measurement setup of the roller cams mover system
was fabricated at Ohtsuka Co.

Fig 5: Conceptual roller cams mover positioning system.

to provide ±1 mm of positioning area. The dark diamondas pictured in Fig. 5 (right) shows the adjustable area,
where each diagonal length is ±1.4 mm in the horizontaland vertical. A mechanical drawing of the roller cams
mover unit is shown in Fig. 6. Two linear sliders are used
to fix the initial positions in horizontal and vertical for theaccelerating structure. We do not use V-blocks and flat
plates fixed to the structure (such as is used in the magnet
positioning roller cams system in the SLAC FFTB).
We measured the maximum adjustable range, andthen a position repeatability of less than ±1 mm anywhere
within the positioning range while loaded with a 50 kg
dummy weight as shown in Fig.7. The position of dummy
weight was measured by the attached electronic
linear-scales as shown in Fig.7. Two roller cams units
were used to manipulate the dummy weight. Each roller
cams mover unit can be controlled individually to adjust
for any axis as shown in Fig. 8. A position repeatabilityof around ±0.1 µm within ± 1 mm of the adjustable area
was obtained.

Figure 8: Deviations of roller cams mover from reference atshort distance.

4 SUMMARY
The new concrete developed for this experimentshows a very high compressive strength, which is 4.4
times higher than conventional concrete, and which isalso higher than natural granite stone. The dry shrinkingvariation curve of the new concrete was almost saturated
at 69 x 10-6 at 13 weeks. The new concrete can be usedwithout any additional reinforcement parts such as theiron reinforcing bars used with existing concrete
structures. The new type roller cams mover systemprovides a position repeatability of ±0.1 µm, within the±1 mm adjusting area. The measured adjustable area
agreed with the expected theoretical results.
From those experimental results, we confirmed thatthe combination of the new concrete and new roller cams
mover system would be suitable for a very precisealignment system.

5 REFERENCES

Figure 6: A cutaway drawing of the roller cams mover unit. 72
mm diameter roller cams give an adjustable range ±1.4 mm.

[1] H. Matsumoto, T. Shintake et. al., “R&D of The C-band RF-system
Development for e+e- Linear Collider in Japan”, 12th Accelerator
Science and Technology, Oct. 1999, RIKEN, JAPAN, KEK
preprint 99-83.
[2] T. Shintake, “SPring-8 Compact SASE Source (SCSS)”, TheInternational Symposium on Optical Science and Technology, 29
July–3 August 2001, San Diego, California, USA[3] R.E. Ruland, “A Design Library of Magnet Supports”, SLAC Pub
7061[4] E. Furse, “Kinematic Design of Fine Mechanisms in Instruments”,
Phys Sci. Instrum. 14 (1981) 246-271.
C-band home page: http://c-band.kek.jp