DEMO physics challenges beyond ITER

• Published in: Fusion engineering and design Vol. 156; p. 111603
• Main Authors: Siccinio, M., Biel, W., Cavedon, M., Fable, E., Federici, G., Janky, F., Lux, H., Maviglia, F., Morris, J., Palermo, F., Sauter, O., Subba, F., Zohm, H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2020; Elsevier Science Ltd
• Subjects: ELM-free regimes; ELMy H-mode; EU-DEMO; Fusion reactors; ITER; Nuclear power plants; Plasma; Plasma (physics); Plasma control; Plasma jets; Plasma scenario; Radiation measurement; Shutdowns; Tokamak devices; Tritium; Plasma scenario; ELMy H-mode; ITER; EU-DEMO; ELM-free regimes
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2020.111603

•EU-DEMO relies on the same plasma scenario as ITER, since this minimizes the risks in the extrapolation.•However, there are some ITER solutions which are not applicable in a DEMO reactor.•This work discusses the DEMO-physics challenges which require a different approach than ITER.•These concern: control of radiative instabilities, divertor detachment control, sawteeth control and adoption of ELM-free regimes. For electricity producing tokamak fusion reactors like EU-DEMO, it is prudent to choose a plasma scenario close to the ITER baseline, where the largest amount of experimental evidence is available. Nevertheless, there are some aspects in which ITER and EU-DEMO have to differ, as the simple exercise of up-scaling from ITER to a larger device is constrained both by physical nonlinearities and by technological limits. In this work, relevant differences between ITER and the current EU-DEMO baseline in terms of plasma scenario are discussed. Firstly, EU-DEMO is assumed to operate with a very large amount of radiative power originating both from the scrape-off layer and, markedly, from the core. This radiation level is obtained by means of seeded impurities, whose presence significantly affects many aspects of the scenario itself, especially in terms of transient control. Secondly, because of the need of breeding tritium, the EU-DEMO wall is less robust than the ITER one. This implies that every off-normal interruption of the plasma discharge, for example in presence of a divertor reattachment, cannot rely on fast-shutdown procedures finally triggering a loss of plasma control at high current, but other strategies need to be developed. Thirdly, the ITER method for the control of the so-called sawteeth (ST) has been shown to be too expensive in terms of auxiliary power requirements, thus other solutions have to be explored. Finally, the problem of actively mitigating, or suppressing, the Edge Localised Modes (ELMs) has recently increased the interest on naturally ELM-free regimes (like QH-mode, I-mode, and also negative triangularity) for EU-DEMO, thus increasing the needs for ELM mitigation or suppression with respect to the approach adopted in ITER.