Towards a compact spherical tokamak fusion pilot plant

Abstract

The question of size of a tokamak fusion reactor is central to current fusion research especially with the large device, ITER, under construction and even larger DEMO reactors under initial engineering design. In this paper, the question of size is addressed initially from a physics perspective. It is shown that in addition to size, field and plasma shape are important too, and shape can be a significant factor. For a spherical tokamak (ST), the elongated shape leads to significant reductions in major radius and/or field for comparable fusion performance. Further, it is shown that when the density limit is taken into account, the relationship between fusion power and fusion gain is almost independent of size, implying that relatively small, high performance reactors should be possible. In order to realize a small, high performance fusion module based on the ST, feasible solutions to several key technical challenges must be developed. These are identified and possible design solutions outlined. The results of the physics, technical and engineering studies are integrated using the Tokamak Energy system code, and the results of a scoping study are reviewed. The results indicate that a relatively small ST using high temperature superconductor magnets should be feasible and may provide an alternative, possibly faster, 'small modular' route to fusion power.

Smaller and quicker with spherical tokamaks and high-temperature superconductors

“…100 MWe), and that these kinds of smaller devices on the development pathway would lead to quicker and cheaper development iterations and faster progress. Costley goes into further detail in his contribution to this meeting [25].…”

“…Some will be proprietary; most will be collaborative. The roadmap is addressed in greater detail by Costley [25]; what follows is a summary of key areas.…”

Can the development of fusion energy be accelerated? An introduction to the proceedings

“…However, the higher fields and operating temperature of high temperature superconductors opens up a new opportunity. Alan Costley's paper [26] in this issue gives in his equation (4.1) the expression for the fusion triple product in terms of tokamak size R 2 0 , toroidal field B 3 T and shape κ 7/2 /A 3 for a tokamak plasma operating under steady-state conditions. It encapsulates the opportunities for smaller tokamaks given by higher field and tighter aspect ratio,…”

“…The two papers by Hartmut Zohm [34] and Alan Costley [26] form a debate on tokamak size that comes to some conclusions. Both agree that toroidal field dependence is crucial to the debate.…”

“…The variation of tokamak major radius (lines) given by lower aspect ratio (x-axis) and by higher magnetic toroidal fields (y-axis). The figure uses the equation shown from Costley's paper [26] in this issue, using the relation Costley noted for the change in elongation (kappa) with aspect ratio. The data are scaled to the ITER operating point.…”