• M. Yoshioka
  KEK, Ibaraki

It was proposed to change from a 2-tunnel scheme in the ILC Reference Design Report to a single tunnel plan by the GDE, Global Design Effort in order to reduce the construction cost. Two proposals of RF source have been presented to realize this scheme. One is 'Klystron Cluster System', which moves every RF source related components from the underground tunnel to the above ground buildings. This would require that the surface topology be rather flat. Another one is the 'Distributed RF System', which does not greatly increase the above ground facilities, and instead every accelerator components are put into a single main tunnel. Instead of powering with large-scale klystrons, downsized modules are distributed throughout. We propose to make a single accelerator tunnel for active accelerator components based on the latter RF system and a sub-tunnel, in which cooling water piping is installed. The sub-tunnel can also be used for the emergency escape, underground water drainage, maintenance work and etc. This scheme fits to the Japanese mountainous site.