LiMeS-Lab: An Integrated Laboratory for the Development of Liquid–Metal Shield Technologies for Fusion Reactors

Journal of Fusion Energy (2023)42:44 https://doi.org/10.1007/s10894-023-00379-3 (0123456789().,-volV)(0123456789(). ,- volV) REVIEW ARTICLE LiMeS-Lab: An Integrated Laboratory for the Development of Liquid– Metal Shield Technologies for Fusion Reactors V. F. B. Tanke1 • R. S. Al1 • S. Alonso van der Westen1 • S. Brons1 • I. G. J. Classen1 • J. A. W. van Dommelen2 • H. J. N. van Eck1 • M. G. D. Geers2 • N. J. Lopes Cardozo3 • H. J. van der Meiden1 • C. A. Orrico3 • M. J. van de Pol1 • M. Riepen4 • P. Rindt3 • T. P. de Rooij3 • J. Scholten1 • R. H. M. Timmer1 • J. W. M. Vernimmen1 • E. G. P. Vos1 • T. W. Morgan1,3 Accepted: 2 August 2023  The Author(s) 2023 Abstract The liquid metal shield laboratory (LiMeS-Lab) will provide the infrastructure to develop, test, and compare liquid metal divertor designs for future fusion reactors. The main research topics of LiMeS-lab will be liquid metal interactions with the substrate material of the divertor, the continuous circulation and capillary refilling of the liquid metal during intense plasma heat loading and the retention of plasma particles in the liquid metal. To facilitate the research, four new devices are in development at the Dutch Institute for Fundamental Energy Research and the Eindhoven University of Technology: LiMeS-AM: a custom metal 3D printer based on powder bed fusion; LiMeS-Wetting, a plasma device to study the wetting of liquid metals on various substrates with different surface treatments; LiMeS-PSI, a linear plasma generator specifically adapted to operate continuous liquid metal loops. Special diagnostic protection will also be implemented to perform measurements in long duration shots without being affected by the liquid metal vapor; LiMeS-TDS, a thermal desorption spectroscopy system to characterize deuterium retention in a metal vapor environment. Each of these devices has specific challenges due to the presence and deposition of metal vapors that need to be addressed in order to function. In this paper, an overview of LiMeS-Lab will be given and the conceptual designs of the last three devices will be presented. Keywords Fusion technology
Plasma-facing components
Liquid metals
Lithium
Tin Introduction Tungsten is considered the baseline divertor plasma facing material (PFM) for many conceptual designs of DEMOscale fusion reactors [1–3]. While for a quiescent and steady plasma and heat load tungsten appears to fulfil the & T. W. Morgan 1 Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ Eindhoven, The Netherlands 2 Department of Mechanical Engineering, Eindhoven University of Technology, Groene Loper 3, 5612 AE Eindhoven, The Netherlands 3 Science and Technology of Nuclear Fusion, Eindhoven University of Technology, Groene Loper 3, 5612 AE Eindhoven, The Netherlands 4 ASML, De Run 6501, 5504 DR Veldhoven, The Netherlands necessary requirements, large edge localized modes (ELMs) and disruptions, combined with the very high neutron loads and operational timelines in such devices, may make long-term operation with such a divertor untenable. Liquid metals (LMs) have been widely studied as alternative PFMs that avoid many of the problems associated with the use of tungsten or other solid PFMs [4]. Liquid tin (Sn) or lithium (Li) are generally considered the leading candidates for this approach. Several recent reviews detail the progress and remaining issues in liquid metal research for fusion [5–7]. One important open question is the development of technological solutions for the application of LMs in fusion reactors. Of main concern is that an open fluid surface is strongly vulnerable to destabilization by magnetohydrodynamic forces which can lead to plasma disruption [8]. Currently several different concepts have been developed and tested to prove the possibility of liquid metals as PFCs. Two main solutions 123 44 Page 2 of 8 are a thermoelectric magnetohydrodynamics driven fast flowing fluid between metal trenches on the PFC [9] and a capillary porous structure (CPS) which holds the metal via capillary pressure [10]. Some possible reactor implementations for these solutions consist of an externally cooled LM filled CPS plate resupplied via a recirculating loop [4]; A box or baffled divertor structure with a high density lithium vapour cloud to cool the plasma while limiting metal vapor flows to the core plasma [11]; and the flowing lithium liquid limiter tested at the EAST tokamak [12]. While the aforementioned concepts have shown promise, compared to current day solid armor walls, LMbased technology is less ready and is technologically more complex. Current levels of knowledge would not be sufficient to confidently introduce this technology to a multibillion Euro large scale fusion reactor. Therefore a stepping stone approach to develop this technology to a higher level of readiness via further scientific and technological investigation and improvement is proposed. To date, although many tokamak experiments using liquid metals have successfully taken place [13–16], experiments with liquid metal divertors in medium and large-scale tokamak experimental facilities are lacking. However, the results from these devices would be the best way to confidently extrapolate to DEMO generation reactors. This lack is mainly due to the absence of well-developed and reliable liquid-metal based divertor plasma-facing components (PFCs). Typically, solid PFC designs are tested in highheat flux and plasma loading facilities [17–19]. However, LM PFCs specifically require high temperature coolants and liquid metal supply loops which do not exist within current facilities of this type, and the liquid metal can contaminate the vacuum systems and diagnostic ports of multi-purpose facilities. Therefore, this project will develop a dedicated liquid metal laboratory which can provide the link between small scale prototype development and larger-scale deployment. Although this project will predominantly focus on the CPS concept for LMPFCs, the laboratory will also be instrumental for studying other LM PFC concepts such as the previously mentioned box divertor and flowing designs. Within this liquid metal laboratory, the current liquid metal CPS divertor concepts can further mature to technology suitable for future reactors, by addressing the following challenges: • Reliably producing tungsten capillary porous structures (CPS) with optimal pore sizes and high strength by means of additive manufacturing. • Wetting and filling of manufactured CPS targets with the liquid metal in order to take advantage of the capillary refilling during operation. 123 Journal of Fusion Energy (2023)42:44 • Liquid surface stability and heat load handling capability of a circulating liquid metal in a CPS target design under plasma exposure. • Retention of hydrogen isotopes by the liquid metal and the prevention of impurity formation in the liquid metal that can result in clogging. The Liquid Metal Shield (...truncated)