We are beginning the new year of 2013 with the draft of the Technical Design Report (TDR) almost complete. The ILC cost estimates are about to be critically reviewed and the organisations such as the International Linear Collider Steering Committee (ILCSC) and the Global Design Effort (GDE) will be handing over responsibility for the leadership of the ILC programme to the new Linear Collider Collaboration, led by Lyn Evans, and to a new oversight group, the Linear Collider Board led by Sachio Komamiya. So what can we expect in 2013 and beyond?
We hope that various governments and related organisations will study the TDR volumes and try to analyse their possible roles in such a global collaboration and project. One predictable outcome will be that several new groups will be asked to review the TDR to report back to their individual governments. This will lead to revisiting many old “what if?” questions and some new ones. I see 2013 as the ‘Year of the “What if”?’.
Some of the questions will be routine,such as “What if you lower the average gradient?” Or alternately, as there has been so much progress with superconducting RF accelerating technology: “What if you raise the average gradient?” A much more complex question which will have to be addressed in the near future is “What if we stage the construction and operation of the ILC beginning at an energy of twice of the Higgs mass, 250 gigaelectronvolt (GeV)?” There are several possible construction and operating schedules that can be considered, and one has to project realistic timelines for desirable physics programmes at the Higgs mass and at higher-energy steps leading up to the baseline energy of 500 GeV. These then should be evaluated along with these alternate accelerator construction schedules.
One option is to build all the baseline facilities but install only what is required for 250 GeV operation. Another is to build only the minimum conventional facilities required for the first stage and complete the construction at a later time. The latter option means only 30% less tunnel, as the whole central region of injectors, damping rings and beam delivery systems are required in all scenarios. Many people are also surprised that construction schedules do not change much because in the Mountain Sites the linac tunnel is constructed in several sections simultaneously. I obviously show my bias towards continuous underground construction because I think stopping and restarting construction might be costly and disruptive of an ongoing physics programme. My thinking is that as we cannot know today what will be the hot topic in the ILC physics programme after a few years with the Higgs, and therefore we need the maximum flexibility by having all the baseline facilities available from the beginning. In fact having the whole baseline ILC would be my first choice —- but “WHAT IF?”