Charting the roadmap to magnetic fusion energy

With the ITER era now well underway, the fusion community is considering the next major steps in magnetic fusion energy (MFE) development. It follows that there is heightened interest worldwide in understanding the roadmap to commercial MFE. In reality, there is no unique roadmap. An important differentiator among possible pathways is risk, i.e. the risks accepted in going from step to step and how risks are mitigated through R&D programs that accompany and support the progression of major nuclear devices. We consider a rollback approach, starting from a definition of what Demo (a power plant that is the last step before commercialization) must accomplish. We assess, in fusion science and technology terms, the mission and requirements for Demo, its prerequisites, and the requirements for a major nuclear devices and the accompanying programs that could precede Demo in order to satisfy its prerequisites. One option for a pre-Demo MFE device is a pilot plant, a facility that would develop and test nuclear components surrounding the plasma, prototype maintenance schemes applicable to a power plant, and demonstrate both tritium self-sufficiency and net electricity generation. An initial assessment of the pilot plant, in terms of its potential to satisfy Demo prerequisites and the associated risks, is presented.