Abstract
Figures of merit for future tokamak fusion power plants (FPPs) are presented. It is argued that extrapolation from present-day experiments to proposed FPPs must follow a consistent development path, demonstrating the largest required leaps in intermediate devices to allow safe extrapolation to an FPP. This concerns both plasma physics and technology. At constant plasma parameters, the figures of merit depend on both major radius R and magnetic field B. We propose to use the term ‘size’ for a combination of R and B to avoid ambiguities in scaling arguments. Two routes to FPPs are discussed: the more conventional one increasing R, based on the assumption that B is limited by present technology; and an alternative approach assuming the availability of new technology for superconducting coils, allowing higher B. It is shown that the latter will lead to more compact devices, and, assuming a criterion based on divertor impurity concentration, is in addition more favourable concerning the exhaust problem. However, in order to obtain attractive steady-state tokamak FPPs, the required plasma parameters still require considerable progress with respect to present experiments. A credible strategy to arrive at these must hence be shown for both paths. In addition, the high-field path needs a demonstration of the critical technology items early on.This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.
Highlights
The development of nuclear fusion as an energy source using magnetic confinement in toroidal geometry has2019 The Authors
We have analysed the size of future tokamak power plants
We have shown that the term ‘size’ involves a combination of the geometrical size and the strength of the confining magnetic field
Summary
In the EU Roadmap, the present assumption is that the physics necessary for the plasma scenario will essentially be demonstrated in ITER, and DEMO is no longer considered an experimental device. These will be formulated using a simple zero-dimensional (0D) model that captures the dependence on the essential plasma physics parameters as well as on the machine parameters. We discuss a route to an FPP based on increasing R, assuming that the value of B is limited by present-day technology. Conclusions are drawn for both development lines
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