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

. In this paper, we study the stability of skyrmions (SKYs) caused by the geometric conﬁnement (GC) effect observed in nano-domains in recent experiments, where SKYs appear only inside the boundary and is stable at the low magnetic ﬁeld region. However, the mechanism of the GC effect is unclear for skyrmions. We numerically ﬁnd that this effect is not observed in the standard model, in which the Dzyaloshinskii-Moriya interaction (DMI) energy is discretized on lattice edges, while the effect is observed in a discrete model where the DMI energy is deﬁned on lattice volume elements. In the latter model, the DMI energy on the surfaces effectively becomes very small compared with that of the inside. From this observation, we study a model with zero DMI energy on the surfaces parallel to the external magnetic ﬁeld and ﬁnd that SKY is signiﬁcantly stabilized in the sample in the low magnetic ﬁeld region.

Effect of Geometric Confinement on the Stabilization of Skyrmions

Visualization method for detecting of residual stress using magnetic domain scope

Magnetic hysteresis curves were calculated using the Monte Carlo method to study the dependence of magnetic properties on the distribution of magnetic sites based on simple diffusion model. The simulated curves illustrate that the magnetic sites distributions influence strongly the magnetic remanence and coercivity depending on diffusion step. Furthermore, the clusters are divided into “colonies”, which are defined as groups of magnetic sites linked by the nearest neighbors, to analyze effect for the hysteresis curves of local structures of magnetic sites in the clusters. These results support that the magnetic sites dispersion system included localized bias determines its magnetic properties depending on the diffusion step, and they would be a new point of view for control of magnetic properties.

Monte Carlo Simulation for Magnetic Granular System with Gaussian Distribution

Evaluation of flux flow resistivity of high Tc superconducting cable for application to fusion reactors

To evaluate the adhesive property of chemical vapor deposit (CVD) diamond coating layer, back‐scattered Rayleigh surface wave method is applied. However, the interpretation of the back‐scattered Rayleigh surface signal is not easy. To take care of such a difficulty, we propose the time trace angular scan (TTAS) method and the frequency spectrum angular scan (FSAS) method to help the interpretation of the back‐scattered Rayleigh surface waves from the CVD diamond coating layer. Using the proposed signal interpretation tools, we evaluate the adhesive property of CVD diamond coating layer. In this paper, the concept of the TTAS and the FSAS methods and the initial experimental results are presented to demonstrate the effectiveness of the proposed approach.

Tetsuya Uchimoto

Papers

Effect of Geometric Confinement on the Stabilization of Skyrmions

Visualization method for detecting of residual stress using magnetic domain scope

Monte Carlo Simulation for Magnetic Granular System with Gaussian Distribution

Evaluation of flux flow resistivity of high Tc superconducting cable for application to fusion reactors

Interpretation of Back-Scattered Rayleigh Surface Wave Signals from Diamond Coating Layers