CRP(2010-2014): Spectroscopic and Collisional Data for W from 1 eV to 20 keV
The choice of materials for the plasma facing components in fusion experiments is guided by competing desirables: on the one hand the material should have a high thermal conductivity, high threshold for melting and sputtering, and low erosion rate under plasma contact, and on the other hand as a plasma impurity it should not cause excessive radiative energy loss. The default choice of material for present experiments is carbon (or graphite), but tritium is easily trapped in carbon-based walls and for that reason carbon is at present held to be unacceptable for use in a D-T fusion experiment such as ITER or in a fusion reactor. In its place, tungsten (symbol W, atomic number 74) is the favoured material for the wall regions of highest particle and heat load in a fusion reactor vessel, with beryllium a possibility for regions of lower heat and particle load. ITER is scheduled to start operation with a W-Be-C wall for a brief initial campaign before switching to W-Be or W alone for the main D-D and D-T experimental programme. In support of ITER and looking ahead to a fusion reactor the Asdex-Upgrade tokamak now operates with an all-W wall, and at JET a full “ITER-like” mixed W-Be-C wall is being installed. Smaller-scale experiments involving tungsten tiles are carried out on other tokamaks. The attractiveness of tungsten is due to its high thermal conductivity, its high melting point, and its resistance to sputtering and erosion, and is in spite of a severe negative factor that as a high-Z plasma impurity tungsten does not become fully stripped of electrons and radiates copiously, so that the tolerable fraction of tungsten impurity in the plasma is at most 2*10-5. Thus, tungsten is the leading candidate for wall material in a fusion reactor, but the radiative properties of tungsten impurity are of great concern and the design of a fusion reactor wall is far from being settled.
The mission of the Nuclear Data Section in the area of atomic and molecular data is to enhance the competencies of Member States in their research into nuclear fusion through the provision of internationally recommended atomic, molecular, plasmamaterial interaction and material properties databases. The Subcommittee on Atomic and Molecular Data of the International Fusion Research Council makes recommendations to the IAEA Nuclear Data Section as to its programme in support of this mission. In its biennial meeting held in April 2008 the Subcommittee recommended that a new CRP on tungsten should be initiated in 2010 as a follow-on to the 2005-2009 CRP on heavy element impurities, but with focus strictly on tungsten data for plasma modelling and diagnostic interpretation and with the goal to provide continued support to the tungsten wall programmes at Asdex-Upgrade and JET. Also, at the final RCM of the heavy element impurities CRP in March 2009 participants agreed that it would be beneficial to initiate another CRP in the future to concentrate on tungsten, in light of the importance of that element in future fusion devices and the extreme complexity of the energy levels of the numerous tungsten ions (75 charge states from neutral to fully stripped). For all these reasons the IAEA agreed to start a CRP on "spectroscopic and collisional data for tungsten from 1 eV to 20 keV". The CRP was formed in the course of 2010 and held its first research coordination meeting 13-15 December 2010.
The CRP is meant to generate fundamental experimental and calculated data for radiative and collisional atomic processes involving tungsten ions interacting with plasma. In general terms the output of the CRP will support the interpretation of spectroscopic measurements on current and future fusion experiments, the modelling of tungsten in fusion plasma, and the design and optimization of fusion reactor experiments. The CRP aims to cover the data needs over the whole range of relevant plasma conditions, ranging from the cool, high-density near-wall plasma to the fusion core, and to cover all the principal collision and radiative processes. Excitation and ionization by electron impact, including multi-stage ionization, auto-ionization, and radiative and dielectronic recombination, together with photon-induced and radiative excitation and de-excitation, are the principal processes that determine the balance of ionization stages in the plasma. Line radiation is the principal energy loss mechanism, and all radiative processes have their distinct spectral properties that are important for interpretation of experimental data. Proton impact processes are relevant in the high density edge plasma, and charge exchange collisions are important in connection with neutral beam plasma heating. The relevant data include cross-sections for kinetic modelling, integrated rate coefficients for macroscopic modelling, and spectroscopic signatures for direct experimental simulations.
Participants and their projects
Nigel BADNELL, University of Strathclyde, Department of Physics: Dielectronic Recombination of Tungsten Ions.
Peter BEIERSDORFER and Joel CLEMENTSON, Lawrence Livermore National Laboratory: Atomic Physics of Tungsten Ions for Magnetic Fusion Diagnostics.
James COLGAN, Los Alamos National Laboratory: Collisional Data Calculations and Collisional-Radiative Modeling for Tungsten.
Chenzhong DONG, Northwest Normal University, College of Physics and Electronic Engineering; Institute of Atomic and Molecular Physics, 967 Anning East Road, 730070 Lanzhou, China: Dielectronic Recombination Cross Sections and Rate Coefficients of Highly Ionized Tungsten Ions.
Fumihiro KOIKE, Kitasato University, School of Medicine, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0374, Japan: Atomic Physics in Weakly, Moderately or Highly Charged Ions of Tungsten Atoms.
Valeriy LISITSA and Alexander KUKUSHKIN, Undertaking of the Developments in Fusion Ldt (UDIF), Oruzheiny 15, Building 1, 125047 Moscow, Russian Federation: Radiative-Collisional Processes in Electron-Tungsten Ion Collisions.
Alfred MÜLLER, Justus-Liebig-Universität Giessen: Crossed- and Merged-Beams Experiments on Tungsten Ion Interactions with Photons and Electrons.
Nobuyuki NAKAMURA, University of Electrocommunications; Institute of Laser Science, Tokyo 182, Japan: Spectroscopic Studies of Highly Charged Tungsten Ions Using Electron Beam Ion Traps (EBITs).
Yuri RALCHENKO, National Institute of Standards and Technology: Experimental and theoretical analysis of EUV and x-ray spectra from highly-charged ions of tungsten.
Alexander RYABTSEV and Rimma KILDIYAROVA, Russian Academy of Sciences, Institute of Spectroscopy, Troitsk: Spectra of W VIII and W IX and Isoelectronic Ions of Hf, Ta and Re.
Rajesh SRIVASTAVA, Indian Institute of Technology at Roorkee: Plasma Based Fully Relativistic Distorted Wave Calculations of Electron Impact Excitation and Ionization Cross Sections and Associated Photon Emissions of Atoms and Ions.
Wan-Ü Lydia TCHANG-BRILLET, Observatoire de Paris, LERMA, and Jean-François WYART, Université Paris Sud: Spectroscopic Properties of Moderately Charged Ions of Tungsten.
Malvina TRZHASKOVSKAYA, Russian Academy of Sciences, St. Petersburg Nuclear Physics Institute and Vladimir K. NIKULIN, Ioffe Physical Technical Institute: Unified Database of Radiative Recombination and Photoionization Cross Sections as Well as Radiative Recombination and Radiated Power Loss Rate Coefficients for Tungsten Ions in Plasmas.
The First Research Coordination Meeting of the CRP took place 13-15 December 2010 at IAEA Headquarters in Vienna. The presentations are available.