The design study is expected to deliver its conclusion in 2018, in time for the next update of the European Strategy. Should the case be still as strong as today, a go-ahead decision could be taken immediately and the tunnel excavation could start at the beginning of the next decade, for a duration of four to eight years, with the simultaneous operation of up to three drilling machines \cite{OsbornePrivate}. The construction and installation of the collider and the detectors would then proceed in parallel with the HL-LHC running for another four to five years. It could thus be technically envisioned, setting aside political, financial, etc., considerations, to start commissioning for the first TLEP physics run as early as in 2030. It will take between a couple months (as at LEP2) and a couple years (as at LEP1) to achieve the design luminosity.

Typically, the baseline physics programme of TLEP would consist of

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  two years at the Z pole (of which one year with the design luminosity of \(5.6~{}{\rm ab}^{-1}\) at each IP, and one year with longitudinal polarization at reduced luminosity), with resonant depolarization of single bunches at intervals of around 20 minutes, for beam energy calibration;

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  one or two years at the WW threshold – with \(1.6~{}{\rm ab}^{-1}\) per year at each IP – with periodic returns at the Z peak (in the TLEP-W conditions) for detector calibration, and with resonant depolarization of single bunches at intervals of around 20 minutes, for beam energy calibration;

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  five years at 240 GeV as a Higgs factory – with \(500~{}{\rm fb}^{-1}\) per year at each IP – with periodic returns at the Z peak (in the TLEP-H conditions);

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  and five years at the \({\rm t}\bar{\rm t}\) threshold – with \(130~{}{\rm fb}^{-1}\) per year at each IP – with periodic returns at the Z peak (in the TLEP-t conditions).

The effective duration of the running at each energy as well as the appropriate order will be defined according to the physics needs and the collider capacities as more knowledge is acquired. Possible luminosity and energy upgrades are not included in this baseline programme. In this aggressive schedule, the VHE-LHC would be installed in the 2040’s, and its physics programme could start in 2050 or thereabout. The TLEP and the VHE-LHC design studies will be conducted in close coordination, with the aim of providing maximum flexibility on concurrent (but not simultaneous) operation and installation of the two machines. Simultaneous operation of an electron (or a positron) beam from TLEP together with a proton beam from VHE-LHC could also be envisioned towards the delivery of high-luminosity ep collisions – up to \(10^{35}~{}{\rm cm}^{-2}{\rm s}^{-1}\) – at high \(Q^{2}\) (VHE-LHeC).