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.

/pdf/plasma-material-interactions-in-current-tokamaks-and-their-1a6iwv89x6.pdf

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

This paper discusses the feasibility of characterizing the shape and size of graphite in flake graphite cast iron based on electromagnetic nondestructive methods. Several flake graphite cast iron specimens containing graphite of various shapes and sizes were prepared and their electromagnetic properties such as conductivity and relative permeability were evaluated systematically. Both the conductivity and the relative permeability were found to mainly depend on the shape and size of graphite. The conductivity was specifically found to have a good correlation with the shape and size of graphite and this was independent of the pearlite area fraction of matrix. The conductivity also correlates well to the ultrasonic velocity which indicates the amount and size of the graphite. The DC potential drop method was used to evaluate the structure of graphite and its capability was evaluated.

Electromagnetic Nondestructive Evaluation of Graphite Structures in Flake Graphite Cast Iron

To explore the mechanism of damage-induced magnetization for paramagnetic austenitic stainless steel, the differ- ences of damage-induced magnetizations between an austenitic stainless steel and a carbon steel are experimentally studied Various plastic strains are introduced into the test-pieces of the austenitic stainless steel of 304 type and S185 carbon steel material The residual plastic strains and the damage-induced magnetic fields nearby the test-pieces, the volume fraction of the damage-induced ferromagnetic martensitic phase in austenitic stainless steel test-pieces are measured The relationships be- tween the residual plastic strain and the damage-induced magnetic field of two materials are investigated and their differences are compared In addition, by establishing the relationships of the damage-induced magnetic field with the damage-induced martensitic phase, the effect of the phase transformation on the damage-induced magnetization of austenitic stainless steel is analyzed

Comparisons of damage-induced magnetizations between austenitic stainless and carbon steel

Eddy current testing (ECT) and ultrasonic testing (UT) have been widely used for the non-destructive testing of metal structures. ECT has a high capability of sizing surface breaking cracks and UT is suitable for sizing sub-surface breaking cracks in thick-wall structures. Based on this background, the authors have proposed a novel dual probe with simple structure combining an electromagnetic acoustic transducer (EMAT) and Eddy current probe. The performance of the probe was verifi ed at room temperature. However, the operating temperature of boiling-water nuclear reactors is 300 degrees C. In this paper, the above dual probe is applied to monitoring of piping wall thinning in a high temperature environment. For this purpose, the structure and components of the probe are discussed so that the present probe should withstand 300 degrees C. Finally, the basic performance of the probe at high temperatures is investigated through an experiment using an electric furnace.

Application of EMAT/EC dual probe to monitoring of wall thinning in high temperature environment

An improved analytical model of the magnetostriction-based EMAT of SH0 mode guided wave in a ferromagnetic plate

Series of slow strain rate tests (SSRT) were conducted on moderately sensitized austenitic stainless steel in diluted aqueous solution of sodium thiosulfate at ambient temperature and pressure. Only a small area of the test piece was exposed to test solution and electrochemical potential transients obtained during the straining was used to detect an initiation or a precursor event of stress corrosion crack (SCC). Tests were stopped intermittently after getting potential transients, so as not to allow crack to propagate and to observe the morphology of very initial stage of SCC initiation site. Visual observation by scanning electron microscope (SEM) before and after the test shows direct correlation between electrochemical transient of certain characteristic to the crack initiation. SEM observation shows δ- ferrite in the alloy as one of the preferential SCC initiation site for typical electrochemical transient. Attempt was made to calculate the charge associated with crack initiation event from potential transient using dummy anode test.

Tetsuya Uchimoto

Papers

Electromagnetic Nondestructive Evaluation of Graphite Structures in Flake Graphite Cast Iron

Comparisons of damage-induced magnetizations between austenitic stainless and carbon steel

Application of EMAT/EC dual probe to monitoring of wall thinning in high temperature environment

An improved analytical model of the magnetostriction-based EMAT of SH0 mode guided wave in a ferromagnetic plate

Understanding and Detecting Early Stages of SCC Initiation in Sensitized Stainless Steel by Means of Electrochemical Potential Transients