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.

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

Progress, since the ITER Physics Basis publication (ITER Physics Basis Editors et al 1999 Nucl. Fusion 39 2137–2664), in understanding the processes that will determine the properties of the plasma edge and its interaction with material elements in ITER is described. Experimental areas where significant progress has taken place are energy transport in the scrape-off layer (SOL) in particular of the anomalous transport scaling, particle transport in the SOL that plays a major role in the interaction of diverted plasmas with the main-chamber material elements, edge localized mode (ELM) energy deposition on material elements and the transport mechanism for the ELM energy from the main plasma to the plasma facing components, the physics of plasma detachment and neutral dynamics including the edge density profile structure and the control of plasma particle content and He removal, the erosion of low- and high-Z materials in fusion devices, their transport to the core plasma and their migration at the plasma edge including the formation of mixed materials, the processes determining the size and location of the retention of tritium in fusion devices and methods to remove it and the processes determining the efficiency of the various fuelling methods as well as their development towards the ITER requirements. This experimental progress has been accompanied by the development of modelling tools for the physical processes at the edge plasma and plasma–materials interaction and the further validation of these models by comparing their predictions with the new experimental results. Progress in the modelling development and validation has been mostly concentrated in the following areas: refinement in the predictions for ITER with plasma edge modelling codes by inclusion of detailed geometrical features of the divertor and the introduction of physical effects, which can play a major role in determining the divertor parameters at the divertor for ITER conditions such as hydrogen radiation transport and neutral–neutral collisions, modelling of the ion orbits at the plasma edge, which can play a role in determining power deposition at the divertor target, models for plasma–materials and plasma dynamics interaction during ELMs and disruptions, models for the transport of impurities at the plasma edge to describe the core contamination by impurities and the migration of eroded materials at the edge plasma and its associated tritium retention and models for the turbulent processes that determine the anomalous transport of energy and particles across the SOL. The implications for the expected performance of the reference regimes in ITER, the operation of the ITER device and the lifetime of the plasma facing materials are discussed.

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Chapter 4: Power and particle control

http://liu.diva-portal.org/smash/get/diva2:303552/FULLTEXT01

The Mn+1AXn phases: Materials science and thin-film processing

SIMNRA is a Microsoft Windows 95/Windows NT program with fully graphical user interface for the simulation of non-Rutherford backscattering, nuclear reaction analysis and elastic recoil detection analysis with MeV ions. About 300 different non-Rutherford and nuclear reactions cross-sections are included. SIMNRA can calculate any ion-target combination including incident heavy ions and any geometry including transmission geometry. Arbitrary multi-layered foils in front of the detector can be used. Energy loss straggling includes the corrections by Chu to Bohr’s straggling theory, propagation of straggling in thick layers, geometrical straggling and straggling due to multiple small angle scattering. The effects of plural large angle scattering can be calculated approximately. Typical computing times are in the range of several seconds.

SIMNRA, a simulation program for the analysis of NRA, RBS and ERDA

The Monte Carlo Program TRIM.SP (sputtering version of TRIM) was used to determine sputtering yields and energy and angular distributions of sputtered particles in physical (collisional) sputtering processes. The output is set up to distinguish between the contributions of primary and secondary knock-on atoms as caused by in- and outgoing incident ions, in order to get a better understanding of the sputtering mechanisms and to check on previous theoretical models. The influence of the interatomic potential and the inelastic energy loss model as well as the surface binding energy on the sputtering yield is investigated. Further results are sputtering yields versus incident energy and angle as well as total angular distributions of sputtered particles and energy distributions in specific solid angles for non-normal incidence. The calculated data are compared with experimental results as far as possible. From this comparison it turns out that the TRIM.SP is able to reproduce experimental results even in very special details of angular and energy distributions.

/pdf/sputtering-studies-with-the-monte-carlo-program-trim-sp-51mc7x1qma.pdf

Sputtering Studies with the Monte Carlo Program TRIM.SP

1. Introduction.- 2. The Binary Collision Model.- 2.1 Laboratory System.- 2.2 Centre-of-Mass System.- 2.3 Relations Between Laboratory and Centre-of-Mass Systems.- 2.4 Energy Transfer.- 2.5 Classical Scattering Theory.- 2.6 Asymptotic Trajectories.- 2.7 Determination of the Scattering Angle and the Time Integral.- 2.8 Limitations of the Binary Collision Approximation.- 2.9 Limitations of the Classical Mechanics Treatment.- 3. Classical Dynamics Model.- 3.1 Newton's Equations.- 3.2 Integration of Newton's Equations.- 3.2.1 Central Difference Scheme.- 3.2.2 Average Force Method.- 3.2.3 Euler-Cauchy Scheme.- 3.2.4 Predictor-Corrector Scheme.- 3.2.5 The Verlet Scheme.- 3.2.6 Nordsieck Method.- 3.3 The Time Step, Bookkeeping.- 4. Interaction Potentials.- 4.1 Screened Coulomb Potentials.- 4.2 The Born-Mayer Potential.- 4.3 Attractive Potentials.- 4.4 Combined Potentials.- 4.5 Empirical Potentials.- 4.6 Embedded Atom Method.- 4.7 Analytical Methods.- 4.8 Comparison of Potentials.- 5. Inelastic Energy Loss.- 5.1 Local Electronic Energy Loss.- 5.2 Continuous Electronic Energy Loss.- 5.3 Comparison.- 6. Thermal Vibrations and Specific Energies.- 6.1 Thermal Vibrations.- 6.2 Specific Energies.- 6.2.1 Cutoff Energy.- 6.2.2 Displacement Energy.- 6.2.3 Bulk Binding Energy.- 6.2.4 Surface Binding Energy.- 7. Programs Based on the BCA Model.- 7.1 Random Target Structures.- 7.2 Monte Carlo Programs.- 7.3 Crystalline Targets.- 7.4 Lattice Programs.- 7.5 TRIM.SP and TRIDYN.- 7.5.1 TRIM.SP.- 7.5.2 TRIDYN.- 7.6 MARLOWE.- 8. Programs Based on the Classical Dynamics Model.- 8.1 Stable, Metastable and Quasi-Stable Programs.- 8.2 Classical Dynamics Programs.- 9. Trajectories.- 10. Ranges.- 10.1 Definitions.- 10.2 Literature.- 10.3 Examples.- 11. Backscattering.- 11.1 Definitions.- 11.2 Literature.- 11.3 Examples.- 12. Sputtering.- 12.1 Definitions.- 12.2 Negative Binomial Distribution.- 12.3 Literature.- 12.4 Examples.- 13. Radiation Damage.- 13.1 Definitions.- 13.2 Component Analysis.- 13.3 Fuzzy Clustering.- 13.4 Literature.- 13.5 Examples.- Abbreviations Used in the Tables.- Constants.- References.- Author Index.

Computer simulation of ion-solid interactions

Based on the sputtering version of the TRIM program for multicomponent targets, a Monte Carlo code has been developed which computes range profiles of implanted ions, composition profiles of the target and sputtering rates for a dynamically varying target composition. It takes into account compositional changes both due to the spatial distribution of target atoms deposited in collision cascades, and due to the presence of the implanted ions. The local density of the target is allowed to relax according to a given function of the densities of the individual components. The applications of the program cover a wide range of problems like the collisional atomic mixing of multilayered targets, dynamic implantation profiles at large fluences, and the fluence-dependent preferential sputtering of multicomponent materials. The present paper provides a description of the program and a critical comparison to similar Monte Carlo codes. As an application, the behaviour of the Ta-C system under He bombardment is studied with respect to sputtering yields, surface composition and composition profiles. Satisfactory agreement is obtained with experimental results given in the literature.

Tridyn — A TRIM simulation code including dynamic composition changes

A review of particle-solid processes pertinent to modelling plasma-wall interactions is presented, and sets of recommended data are given. Analytic formulas are used where possible; otherwise, data are presented in the form of tables and graphs. The incident particles considered are e−, H, D, T, He, C, O, and selfions. The materials include the metals aluminum, beryllium, copper, molybdenum, stainless steel, titanium, and tungsten and the nonmetals carbon and TiC. The processes covered are light ion reflection, hydrogen and helium trapping and detrapping, desorption, evaporation, sputtering, chemical effects in sputtering, blistering caused by implantation of helium and hydrogen, secondary electron emission by electrons and particles, and arcing.

W. Eckstein

Papers

Computer simulation of ion-solid interactions

Sputtering Studies with the Monte Carlo Program TRIM.SP

Tridyn — A TRIM simulation code including dynamic composition changes

Data Compendium for Plasma-Surface Interactions

Sputtering by Particle Bombardment