ILC CONVENTIONAL FACILITY IN ASIAN SITES
Atsushi Enomoto and M. Miyahara, KEK, Tsukuba, JapanAbstract
The international linear collider (ILC) is on a stage ofpreparing technical design report (TDR). Through value
engineering to reduce civil construction costs, the tunnel
configuration was changed from double- tunnel scheme tosingle. The double-tunnel scheme accommodates
superconducting accelerator modules and their power
supplies independently. This is a very natural scheme forsetting an accelerator and its power supply nearby and forpreventing radiation damage of the power supply.
However, the single-tunnel scheme was proposed toreduce cost, and to avoid such radiation problem threekinds of high-level RF (HLRF) systems are proposed. We
report the comparison of ILC main linac costs andconstruction schedules between eight cases for
combinations of diferent tunnel excavation methods andHLRF systems; then, we report the potential facility
design for the Asian sites.

INTRODUCTION
The ILC will be an electron-positron beam collider
composed of seven individual systems: an electron (e-)
and a positron (e+) source, damping rings (DRs), ring-tomain-linac (RTML) for beam transport, the main linacs(MLs), beam delivery system (BDS), and detector hall
(DH). The DRs, RTML, MLs, and BDS will be installedin each e- and e+ accelerator sides. The total length of theaccelerator will be approximately 30 km and will be
operating at a centre-of-mass collision energy of 500 GeV.
The e- source, the e+ source, DRs, BDS, and DH will belocated at the central region of the ILC.

SITE LAYOUT
The Asian region civil design has the following sitespecific features since it is to be constructed on hard
bedrock of deep underground at one of the Japanesemountainous site candidates: The ML tunnel meets the requirement for distributed
klystron system (DKS).
 Instead of TBM (tunnel boring machine), NATM
(New Austrian Tunneling Method) is employed.
 The underground structures are divided into sevenareas along ILC with a maximum span of +-2.5 km.
 Instead of vertical shafts, access tunnels (ATs) with aslope are used to access the underground halls (AHs).
 Some surface facilities are moved into underground.
The Asian site overall site layout is shown in Fig. 1.
The ML consists of 285 (e-) and 282 (e+) RF units. For
DKS, the ML cryomodule configuration is based on the 9module string as shown in Fig. 2.

Figure 1: Overall site layout in the Asian site.

Figure 2: Cryogenic system configuration and cryogenic plant location in the Asian site.

CIVIL DESIGN
Main Linac Tunnel
To investigate the tunnel construction cost and schedule,
the following eight cases (Fig. 3) are studied regarding
tunnel excavation methods (TBM or NATM) and single
tunnel configurations.
 Cases 1 to 5 use TBM and cases 6 to 8 use NATM.
 Cases 1 to 5 compare facilities with different HLRF
systems (RDR, XFEL, KCS, and DRFS).
 Cases 6 and 8 compare single tunnel with auxiliary
small tunnel and with centre walls.
By this study it was seen that a single tunnel excavatedby NATM is most cost effective in Asian site. Although
we have further advantages such as flexible excavation oftunnel section and less construction risk, an obvious
disadvantage is the slower excavation speed (~100m/month) of NATM. However, this disadvantage could bemitigated in the following way. NATM does not needsuch preparation time as required in TBM commissioning.
A short-distance excavation is not cost-effective in TBM
but not the case in NATM. Thus parallel work can be
conducted in shorter construction zone and the NATM is
not necessarily slower than TBM in the Asian site.

maximum of 2 m forward the service tunnel direction up
to the front end of the modulator rack. The shield effect ofthe wall and passage way was simulated assuming a beamloss and referring to a radiation safety regulation.

Figure 4: “Kamaboko”-shape section of ML tunnel.

Figure 5: Passage way between beam and service tunnels.

Big size caverns
Figure 3: Tunnel configuration variance for case study.
The ML tunnel section is divided by a centre wall into
beam and service tunnel as shown in Fig.4. Each tunnel
section has functional zones for the equipment installation,survey, conveyance, and human egress. In each tunnel,
the right side of accelerator equipment (cryomodule andmodulator) is equipment-conveyance and human-egresszone. The left-side of the equipment is working space but
used as a detour even if the egress zone is occupied byequipment. The water pipes are installed basically inlower part. The electric power lines are installed in(shielded) cable racks hanging at the ceiling. Taking aconsideration of these configurations, a necessary tunnel
width is 7.5 m at minimum except the centre shield wall.
The centre wall is necessary for the radiation shield toprotect human in the service tunnel. The foot thickness ofthe wall is 3.5 m and the upper side thickness is 2 m. In
every 3-4 rf units at the empty area of modulators, aconnection passage between the beam and service tunnels
is constructed (Fig.5). This is used for evacuation ofhuman from accident to opposite side. For the passage
way, the centre wall thickness can be increased by a

The AH and DH sizes are similar to those ofunderground hydroelectric power plants in Japan. Since
the detector hall access is not by vertical shaft used at
LHC but by a sloped tunnel, the design is underway
taking account of assembly, operation, and maintenanceprocess for two push-pull detectors (Fig.6)

Figure 6: Detector hall designs.

ELECTRICAL DESIGN
The power (216 MW) is distributed in three stages:
 The site electric power is stepped down from highvoltages (150-500 kV) to 66 kV in the main
substation and distributed to seven undergroundhalls (6 AHs, 1 DH)).
 The 66-kV electricity is further stepped down to 6.6
kV at each AH/DH substations and distributed local
areas withn +-2.5 km.
 RF modulators and cryogenic warm compressors are
powered directly at 6.6 kV and low voltages are
stepped down from 6.6 kV in local substations.
The main substation diagram is given in Fig. 7: Four 100MW transformers (including one back-up) are installedwith spaces for the two for future 1 TeV upgrade. The
capacity of the access hall 66/6.6-kV transformers isequalized to be two 30-MW by reasons of maintenance.

service tunnel. The system is the same as in Fig.9 except
using refrigerator. Tunnel inflow water is utilized for themakeup water for cooling towers as shown in Fig. 10.
Flesh ambient air cooled/dehumidified in summer andheated in winter, kept 29C and 35%, .is supplied to theunderground by large-bore ducts through access tunnels.
The air blows in the tunnel without ducts at a flow rate of~0.5 m/s.

Figure 9: Cooling-water system.

Figure 7: Main substation single-line diagram.

MECHANICAL DESIGN
The mechanical design is based on the heat-load
criteria collected from the technical group as shown in Fig.
8. The criteria are integrated in each seven undergroundarea. Figures 9 and 10 are the typical mechanical designs
for the cooling-water system and piped utilities at an AH.

Figure 10: Piped utilities.

Figure 11: Air ventilation system.
Figure 8: An example of heat load table (ML).
The cooling-water system is based on 3-loop systemand the third-loop temperature cooling equipment is 34C
in supply and 45C in return. Child water (7C supply and18C return) is used to cool instrument racks and the air ofREFERENCES[1] A. Enomoto et al., “The Asian regional proposal for asingle-tunnel configuration for the conventional facility”,
Linac2010, Tsukuba, Japan, July 2004, MPO028, p.115.