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.)

Full text

PREPARED FOR THE U.S. DEPARTMENT OF ENERGY,
UNDER CONTRACT DE-AC02-76CH03073
PRINCETON PLASMA PHYSICS LABORATORY
PRINCETON UNIVERSITY, PRINCETON, NEW JERSEY
PPPL- 3531 PPPL- 3531
IPP- 9/128 IPP- 9/128
UC-70
Plasma-material Interactions in Current Tokamaks
and their Implications for Next-step Fusion Reactors
by
Gianfranco Federici, Charles H. Skinner, Jeffrey N. Brooks, Joseph Paul Coad,
Christian Grisolia, Anthony A. Haasz, Ahmed Hassanein, Volker Philipps,
C. Spencer Pitcher, Joachim Roth, William R. Wampler, and Dennis G. Whyte
January 2001
A joint report with theA joint report with the
A joint report with theA joint report with the
A joint report with the
Princeton Plasma Physics Laboratory (Princeton, NJ USA)Princeton Plasma Physics Laboratory (Princeton, NJ USA)
Princeton Plasma Physics Laboratory (Princeton, NJ USA)Princeton Plasma Physics Laboratory (Princeton, NJ USA)
Princeton Plasma Physics Laboratory (Princeton, NJ USA)
and the Max-Planck-Institut für Plasmaphysik, (Garching, Germany)and the Max-Planck-Institut für Plasmaphysik, (Garching, Germany)
and the Max-Planck-Institut für Plasmaphysik, (Garching, Germany)and the Max-Planck-Institut für Plasmaphysik, (Garching, Germany)
and the Max-Planck-Institut für Plasmaphysik, (Garching, Germany)

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Plasma-material interactions in current tokamaks and
their implications for next-step fusion reactors.
Gianfranco Federici
∗
ITER Garching Joint Work Site, Boltzmannstraße 2, 85748 Garching, Germany.
Charles H. Skinner
†
Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA.
Jeffrey N. Brooks
‡
Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439, USA.
Joseph Paul Coad
JET Joint Undertaking, Abingdon, Oxfordshire, OX14 3EA, UK.
Christian Grisolia
Tore Supra, CEA Cadarache, F-13108 St Paul lez Durance, Cedex, France.
Anthony A. Haasz
§
University of Toronto, Institute for Aerospace Studies, Toronto, Ontario, M3H 5T6, Canada.
Ahmed Hassanein
¶
Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439, USA.
Volker Philipps
Institut fuer Plasmaphysik, Forschungzentrum Juelich, D-52425 Juelich, Germany.
C. Spencer Pitcher
k
MIT Plasma Science and Fusion Center, 175 Albany Street - Cambridge, MA, 02139, USA.
Joachim Roth
Max-Planck-Institut fuer Plasmaphysik, D-85748 Garching, Germany.
William R. Wampler
∗∗
Sandia National Laboratories, Albuquerque, NM 87185, USA.
Dennis G. Whyte
††
University of California San Diego, La Jolla, California 92093-0417, USA.
∗
corresponding author: e-mail: federig@ipp.mpg.de, tel. +49-89-32994228; fax. +49-89-32994110.
†
supported by the United States Department of Energy under Contract DE-AC02-76CH03073.
‡
supported by the United States Department of Energy under Contract W-31-109-Eng-38.
§
supported by the Natural Sciences and Engineering Research Council of Canada and ITER Canada.
¶
supported by the United States Department of Energy under Contract W-31-109-Eng-38.
k
supported by the United States Department of Energy under Contract DE-FC02-99ER54512.
∗∗
supported by the United States Department of Energy under Contract DE-AC04-94AL85000.
††
supported by the United States Department of Energy under Grant No. DE-FG03-95ER54301.
1

G. Federici, C.H. Skinner, et al.
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 in to sharp focus in
the process of designing of 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 under-
standing 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 author-
itative 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 email 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 pre-print by the Max-Plank-Institut fuer Plasma Physik
at Garching and the Princeton Plasma Physics Laboratory. 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.
2 (January 2001)

Review: Plasma-material interactions
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 influ-
ence its operation, safety and performance. Erosion will increase to a scale of several cm 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 co-ordinated effort in the field of plasma-surface interactions supporting
the Engineering Design Activities of the International Thermonuclear Experimental Reac-
tor project (ITER) and significant progress has been made in better understanding these
issues. This paper reviews the underlying physical processes and the existing experimen-
tal 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/re-deposition 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 con-
ditions expected in future devices is explained. Outstanding technical issues and specific
recommendations on potential R&D avenues for their resolution are presented.
Contents
1. INTRODUCTION/BACKGROUND 18
1.1. Introduction..................................... 18
1.2. Plasma-Edge Parameters and Plasma-Material Interactions . . . . . . . . . . 19
1.2.1. Plasmainteractionwiththedivertor................... 20
1.2.2. Additionaldivertorfunctions ....................... 21
1.2.3. Plasmainteractionwiththemain-chamberwall............. 22
1.2.4. Physical and chemical sputtering and its consequences . . . . . . . . . 23
1.3. HistoryofPlasma-FacingMaterials........................ 24
1.3.1. Limiteranddivertortokamaks ...................... 25
1.3.2. Plasma-facingmaterials .......................... 26
2. PLASMA-EDGE AND PLASMA-MATERIAL INTERACTION ISSUES
IN NEXT-STEP TOKAMAKS 33
2.1. Introduction..................................... 33
2.2. ProgressTowardsaNext-StepFusionDevice .................. 33
2.2.1. Advances in today’s fusion devices and prospects . . . . . . . . . . . . 33
2.2.2. Distinctivefeaturesofanext-steptokamak ............... 36
2.3. Most Prominent Plasma-Material Interaction Issues for a Next-Step Fusion
Device........................................ 37
2.3.1. Powerdispersalanddensitycontrol ................... 37
2.3.1.1. Power dispersal and removal .................. 37
(January 2001) 3

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.