Plasma{material interactions in current tokamaks and their implications for next step fusion reactors

TLDR: In this article, the authors review 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.

Abstract: The major increase in discharge duration and plasma energy in a next step DT 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 centimetres 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 stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER), and significant progress has been made in better understanding these issues. The 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 interaction are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation and (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 avenues for their resolution are presented.

Figures

Figure 53. Volume average density evolution for very long discharges in Tore Supra; (reproduced with permission from [652].)

Figure 20. (a) Fluence dependence of the deposited depth for W bombarded with deuterium ions from a 20 eV divertor plasma with various levels of carbon impurities; (reproduced with permission from [335]). (b) Boundaries of erosion and deposition conditions for W bombarded with deuterium ions depending on plasma electron temperature, Te, and carbon impurity content, f ∗ c . The four possible time developments (A-D) are schematically indicated in the figure in their region of validity; (reproduced with permission from [335].)

Figure 54. Removal of H2 by ICRH plasmas from the first-wall of TEXTOR. 1 Pa·m3 = 2.7x1020 molecules; (reproduced with permission from [41].)

Figure 7. High-heat-flux test results: Heat flux vs. number of cycles for prototypical W/Cu and Be/Cu high-heat-flux components; (figure provided by M. Ulrickson Sandia National Laboratory [256].)

Figure 71. Rate of tritium release during air exposure of the torus at ambient temperature following the JET DTE1 campaign; (reproduced with permission from [203].)

Figure 85. Results from a B2/EIRENE simulation of the ITER edge plasma [829]. r-rsep is the distance from the last closed flux surface (outside mid-plane equivalent); (figure provided by A. Kukushkin, ITER.)

Frequently asked questions

Q1. What have the authors contributed in "Prepared for the u.s. department of energy, under contract de-ac02-76ch03073 princeton plasma physics laboratory princeton university, princeton, new jersey" ?

Recognition of the important consequences of these phenomena has stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project ( ITER ) 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. 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 avenues for their resolution are presented. 

Q2. What future works have the authors mentioned in the paper "Prepared for the u.s. department of energy, under contract de-ac02-76ch03073 princeton plasma physics laboratory princeton university, princeton, new jersey" ?

Although the field is rapidly evolving and the present review is one of work in progress, some key conclusions relevant to a next-step device are presented below, together with some recommendations for future work. 

Q3. What was the main theme of the paper?

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. 

Q4. What are the main topics of interactions in the paper?

Two main topical groups of interactions are considered: (i) erosion/re-deposition from plasma sputtering and disruptions, including dust and flake generation, (ii) tritium retention and removal. 

Q5. What is the main theme of the paper?

PREFACEManaging the interface between a burning plasma and the material world has long been regarded as one of the grand challenges of fusion. 

Q6. What is the importance of controlling plasma wall interactions in tokamaks?

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. 

Q7. What is the main topic of the paper?

Recognition of the important consequences of these phenomena has stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER) and significant progress has been made in better understanding these issues. 

Q8. What was the important factor in the review?

What the authors naively underestimated was a quantity increasingly scarce in the world today, the time needed to weld the material into a coherent whole.