Plasma-material Interactions in Current Tokamaks and their Implications for Next-step Fusion Reactors
Authors: Gianfranco Federici, Charles H. Skinner, Jeffrey N. Brooks, Joseph Paul Coad, Christian Grisolia, Anthony A. Haasz, Ahmed Hassanein, Volker Philipps, C. Spencer Pitcher, Joachim Rothe, William R. Wampler, and Dennis G. Whyte
Date of PPPL/IPP Report: January 2001
Published by: Nuclear Fusion 41, No. 12R (December 2001) 1967-2137.
Preface: Managing the interface between a burning plasma and the material world has long been regarded as one of the grand challenges of fusion. The issues came into sharp focus in the process of designing of the International Thermonuclear Experimental Reactor (ITER). It also became clear that the diversity of phenomena at work in plasma-surface interactions had led to compartmentalisation -- specialists were active within their areas but the issues often demanded integrated solutions that transcended the boundaries of individual disciplines. The link between the condition of plasma-facing surfaces and plasma performance was experimentally obvious to all, but the lack of an easily accessible up-to-date overview fostered lingering suspicions of "kitchen physics" at the plasma boundary.
Three years ago we conceived a review that would make accessible the progress in understanding the physics of plasma-material interactions and the strong implications for next-step devices. An international group of co-authors joined together to provide the most authoritative overview of the different areas. What we naively underestimated was a quantity increasingly scarce in the world today, the time needed to weld the material into a coherent whole. Electronic communication, especially e-mail attachments, proved to be an essential tool to facilitate input and integrate material from co-authors spread over the globe.
The review is aimed for publication in Nuclear Fusion. We are making the material immediately accessible in a joint preprint by the Max-Plank-Institut fuer Plasmaphysik at Garching and the Princeton Plasma Physics Laboratory, Princeton, NJ, USA. The review is lengthy but we have structured the material so that a busy reader can skip immediately to the topic of his or her immediate interest and branch from there to other relevant areas. We hope we have illuminated the physics of plasma-material interactions for specialists in other areas of magnetic fusion and that together, we will continue to foster progress toward solutions to the long-term energy needs of mankind.
Gianfranco Federici -- ITER,
Charles Skinner -- PPPL,
Joachim Roth -- IPP-Garching.
Abstract: The major increase in discharge duration and plasma energy in a next-step DT [deuterium-tritium] fusion reactor will give rise to important plasma-material effects that will critically influence its operation, safety, and performance. Erosion will increase to a scale of several centimeters from being barely measurable at a micron scale in today's tokamaks. Tritium co-deposited with carbon will strongly affect the operation of machines with carbon plasma-facing components. Controlling plasma wall interactions is critical to achieving high performance in present-day tokamaks and this is likely to continue to be the case in the approach to practical fusion reactors. Recognition of the important consequences of these phenomena has stimulated an internationally coordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor (ITER) project and significant progress has been made in better understanding these issues. This paper reviews the underlying physical processes and the existing experimental database of plasma-material interactions both in tokamaks and laboratory simulation facilities for conditions of direct relevance to next-step fusion reactors. Two main topical groups of interactions are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation, (ii) tritium retention and removal. The use of modelling tools to interpret the experimental results and make projections for conditions expected in future devices is explained. Outstanding technical issues and specific recommendations on potential R&D [Research and Development] avenues for their resolution are presented.