Modular fusion power plant

Pulsed Spherical Tokamak—A New Approach to Fusion Reactors

Traditionally, spherical tokamak (ST) reactors are considered to operate in a steady state. This paper analyses the advantages of a pulsed ST reactor. The methodology developed for conventional tokamak (CT) reactors is used and it is shown that advantages of a pulsed operation are even more pronounced in an ST reactor because of its ability to operate at a higher beta, therefore achieving a higher bootstrap current fraction, which, together with a lower inductance, reduces requirements for magnetic flux from the central solenoid for the plasma current ramp-up and sustainment.

Towards a compact spherical tokamak fusion pilot plant

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. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.

Compact steady-state tokamak performance dependence on magnet and core physics limits

Compact tokamak fusion reactors using advanced high-temperature superconducting magnets for the toroidal field coils have received considerable recent attention due to the promise of more compact devices and more economical fusion energy development. Facilities with combined fusion nuclear science and Pilot Plant missions to provide both the nuclear environment needed to develop fusion materials and components while also potentially achieving sufficient fusion performance to generate modest net electrical power are considered. The performance of the tokamak fusion system is assessed using a range of core physics and toroidal field magnet performance constraints to better understand which parameters most strongly influence the achievable fusion performance. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.

Smaller and quicker with spherical tokamaks and high-temperature superconductors

Research in the 1970s and 1980s by Sykes, Peng, Jassby and others showed the theoretical advantage of the spherical tokamak (ST) shape. Experiments on START and MAST at Culham throughout the 1990s and 2000s, alongside other international STs like NSTX at the Princeton Plasma Physics Laboratory, confirmed their increased efficiency (namely operation at higher beta) and tested the plasma physics in new regimes. However, while interesting devices for study, the perceived technological difficulties due to the compact shape initially prevented STs being seriously considered as viable power plants. Then, in the 2010s, high-temperature superconductor (HTS) materials became available as a reliable engineering material, fabricated into long tapes suitable for winding into magnets. Realizing the advantages of this material and its possibilities for fusion, Tokamak Energy proposed a new ST path to fusion power and began working on demonstrating the viability of HTS for fusion magnets. The company is now operating a compact tokamak with copper magnets, R0 ∼ 0.4 m, R/ a ∼ 1.8, and target Ip = 2MA, Bt0 = 3 T, while in parallel developing a 5 T HTS demonstrator tokamak magnet. Here we discuss why HTS can be a game-changer for tokamak fusion. We outline Tokamak Energy's solution for a faster way to fusion and discuss plans and progress, including benefits of smaller devices on the development path and advantages of modularity in power plants. We will indicate some of the key research areas in compact tokamaks and introduce the physics considerations behind the ST approach, to be further developed in the subsequent paper by Alan Costley. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.