There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

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

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

The MAX phases are a group of layered ternary compounds with the general formula Mn+1AXn (M: early transition metal; A: group A element; X: C and/or N; n = 1–3), which combine some properties of metals, such as good electrical and thermal conductivity, machinability, low hardness, thermal shock resistance and damage tolerance, with those of ceramics, such as high elastic moduli, high temperature strength, and oxidation and corrosion resistance. The publication of papers on the MAX phases has shown an almost exponential increase in the past decade. The existence of further MAX phases has been reported or proposed. In addition to surveying this activity, the synthesis of MAX phases in the forms of bulk, films and powders is reviewed, together with their physical, mechanical and corrosion/oxidation properties. Recent research and development has revealed potential for the practical application of the MAX phases (particularly using the pressureless sintering and physical vapour deposition coating rout...

Progress in research and development on MAX phases: a family of layered ternary compounds

Nondestructive evaluation of plastic damage in a RAFM steel considering the influence of loading history

Fusion plasma engineers have made remarkable progress in designing a tokamak type of experimental reactor, as evidenced by the International Thermonuclear Experimental Reactor (ITER), which produces fusion energy of 1.5 GW(thermal) for 1000 s at least. However, the ITER design is more expensive and requires more advanced technology than earlier machines. With these concerns in mind, extending design options by using a high-temperature superconductor (HTSC) to improve plasma positional instability by placing HTSC ring coils inside the vacuum vessel would be desirable. Here, improving the plasma instability with HTSC coils is discussed, and a possible design ofa smaller machine using the coils based on supporting experiments with HTSC tapes is given.

Application of high-temperature superconductors to enhance nuclear fusion reactors

This paper demonstrates the crack detection of thick-walled non-magnetic metal plates by eddy current testing, which is difficult because of Kelvin skin effect generally. The purpose of this research is the development of an new eddy current testing probe for cracks in thick-walled plates and crack shapes quantitative evaluation. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of this new probe are strong eddy current on the back of specimens and gentle decrement of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect with 0.5 mm thickness on IN-CONEL 718 specimen with 7.0 mm thickness. Reconstruction of crack shapes was performed based on the experimental results with the inverse problem code developed by authors. The length and depth of reconstructed defects approximately agree with those of real crack.

Development of Eddy Current Testing Probe for Thick-Walled Metal Plate and Quantitative Evaluation of Crackes.

Two types of cast iron materials—flake graphite cast iron and ductile cast iron—were investigated by the method of magnetic adaptive testing, which is based on the systematic measurement and the evaluation of minor magnetic hysteresis loops. In all cases, even within the same type of material rather big differences existed considering both the chemical composition and the material structure of the investigated sample series. The matrix structure was determined by traditional metallographic examination, and these values were compared with the non-destructively measured magnetic parameters. It was shown that the relative pearlite volume fraction of the metallic matrix of cast iron samples could be determined by this method with a good reliability. The same is true also for the relative chill content of the matrix, as long as the samples contain chill at all. A general expression was found to characterize those correlations, which do not depend on the actual sample and neither on the applied parameters of the concrete magnetic measurement.

Investigation of Cast Iron Matrix Constituents by Magnetic Adaptive Testing

The method of magnetic adaptive testing (MAT) was applied for the investigation of flake graphite cast iron samples having various metallic matrix and graphite structures MAT is typical by its low required magnetization of samples, because it is based on the measurement of families of minor magnetic hysteresis loops The flat samples were magnetized by an attached yoke and sensitive descriptors of their magnetic/structural state were obtained from the evaluation of the measured data Metallographic examination of the matrix and graphite structures was performed and results of the nondestructive magnetic tests were compared with these data A very good correlation was found between the magnetic descriptors and the graphite morphology With these results, MAT is suggested as a highly promising nondestructive alternative of destructive tests for monitoring structural changes in cast iron and other ferromagnetic objects

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Tetsuya Uchimoto

Papers

Nondestructive evaluation of plastic damage in a RAFM steel considering the influence of loading history

Application of high-temperature superconductors to enhance nuclear fusion reactors

Development of Eddy Current Testing Probe for Thick-Walled Metal Plate and Quantitative Evaluation of Crackes.

Investigation of Cast Iron Matrix Constituents by Magnetic Adaptive Testing

Flake Graphite Cast Iron Investigated by a Magnetic Method