The International Linear Collider Machine Staging Report 2017

The Technical Design Report (TDR) of the ILC mainly concentrates on a baseline machine of 500 GeV centre-of-mass with detailed cost and manpower estimates consistent with this option. However, the discovery of a Higgs Boson with a mass of 125 GeV opens up the possibility of reducing cost by starting at a centre-of-mass energy of 250 GeV with the possibility of future upgrades to 500 GeV or even 1 TeV should the physics case for such an upgrade be compelling. The rest of this paper outlines the options for the design of a 250 GeV Higgs factory”. The scientific programme that the machine would offer is the subject of a separate report.