Fundamental understanding of Plasma Surface Interaction (PSI) processes in magnetic and inertial confinement fusion devices requires dedicated R&D activities in close connection with material characterization as well as with theory and modelling. There are many gaps in the field of PSI which must be addressed in order to develop the predictive capability in support of the design of the plasma facing components for the world’s largest fusion experiment in southern France, ITER, and for a future fusion demonstration power plant (DEMO). Although a number of unresolved issues on plasma edge physics in magnetic confinement devices (e.g. scrape-off layer plasma widths, flows and turbulent transport) can only be addressed using tokamaks and stellarators, some other issues related to the impact of transient heat loads on materials, erosion and redeposition mechanisms, fuel retention, dust formation, as well as new material concepts can be explored using dedicated test bed devices. In fact, besides providing a good access to the plasma material interaction zone, allowing the specific diagnostics to be operational and an easy exchange of material samples, the reasons to explore the field of PSI using test bed facilities include the ability to:
- Provide ITER relevant particle and energy fluxes (high density and low energy semi-detached plasma);
- reach ITER relevant fluence;
- reproduce ITER relevant transient heat loads (edge localized modes, disruptions) not achievable in today’s tokamaks but achievable in today’s plasma accelerators;
- make single parameters and single process parametric studies which are not possible in tokamaks;
- provide well diagnosed test cases for benchmarking plasma wall interaction codes, as well as test beds for PSI diagnostics;
- study combined effects of heat load and neutron damage on materials in dedicated facilities; and
- be robust in design and cost effective.
The purpose of the CRP – organized and conducted from 2011 to 2016 – was to plan and coordinate activities addressing relevant issues associated with the impact of intense transient heat and particle loads on plasma facing materials. Candidate plasma facing materials for next-step fusion devices include tungsten (diverter and first wall), beryllium (first wall in ITER), and various types of ceramics and transparent materials as functional materials for insulation and diagnostics. The CRP has paid particular attention to investigating different grades of tungsten as material to be used in the most loaded areas in ITER and as the current primary choice in DEMO plasma facing material.
In order to address the issue, the CRP has made use of the existing network of test bed devices such as dense plasma foci, plasma accelerators and particle accelerators, electron beam facilities and nuclear fission reactors, in which it is possible to reproduce particles and heat load conditions expected in fusion reactors. The CRP has provided input into the knowledge-based understanding of the underlying processes leading to material damage due to heat and neutron loads in fusion devices, while contributing to the development of fusion technology.
In particular, this CRP has promoted the use of small-scale devices as test bed facilities to address issues of high relevance for large scale fusion devices. Activities have led to increased capabilities of diagnostics for plasma material interaction. In addition, it made it possible for countries not currently members of the ITER project to contribute to ITER-relevant scientific investigations. It also provided opportunities for scientific cooperation among developed and developing countries. A remarkable impact has been made in honing the capabilities of young scientists in fusion relevant research in participating countries.
The subject of materials under extreme conditions has applications in several research and industrial areas. The work performed in the framework of the CRP has relevance beyond its original scope (for example materials for aerospace applications, high temperature engineering, and novel plasma technologies).
A total of 18 institutions with researchers from Bulgaria, Chile, the Czech Republic, Estonia, Germany, India, Iran, Italy, Kazakhstan, Malaysia, the Netherlands, Poland, Russia, Singapore and Ukraine participated in this CRP.
The results of the five-year CRP were published in TECDOC: https://www-pub.iaea.org/MTCD/Publications/PDF/TE1829_web.pdf
For more information, please see the CRP description:
https://www.iaea.org/projects/crp/f13013