361 research outputs found
Effect of the surface temperature on surface morphology, deuterium retention and erosion of EUROFER steel exposed to low-energy, high-flux deuterium plasma
Samples of EUFROFER, a reduced activation ferritic martensitic steel, were exposed in the linear plasma device Pilot-PSI to a deuterium (D) plasma with incident ion energy of similar to 40 eV and incident D flux of 2-6 x10(23) D/m(2) s to fluences up to 10 27 D/m(2) at surface temperatures ranging from 400 K to 950 K. The main focus of the study lays on the surface morphology changes dependent on the surface temperature and the surface composition evolution, e.g., the enrichment in tungsten; but also the erosion and the D retention are studied. The created surface morphology varies strongly with surface temperature from needle-like to corral-like structures. The visible lateral length scale of the formed structures is in the range of tens of nanometres to above 1 mu m and exhibits two thermal activated regimes below and above similar to 770 K with activation energies of 0.2 eV and 1.3 eV, respectively. The lateral variation of the enrichment of heavy elements on the surface is correlated to this surface morphology at least in the high temperature regime, independent of the origin of the enrichment (intrinsic from the sample or deposited by the plasma). Also the erosion exhibits temperature dependence at least above similar to 770 K as well as a fluence dependence. The amount of deuterium retained in the top 500 nm is almost independent of the exposure temperature and is of the order of 10(18) D/m(2), which would correspond to a sub-monolayer D coverage on the surface. The retained D in the volume summing up over the complete samples exceeds the D retained close to the surface by one order of magnitude. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Dissociative recombination and electron-impact de-excitation in CH photon emission under ITER divertor-relevant plasma conditions
For understanding carbon erosion and redeposition in nuclear fusion devices,
it is important to understand the transport and chemical break-up of
hydrocarbon molecules in edge plasmas, often diagnosed by emission of the CH
A^2\Delta - X^2\Pi Ger\"o band around 430 nm. The CH A-level can be excited
either by electron-impact or by dissociative recombination (D.R.) of
hydrocarbon ions. These processes were included in the 3D Monte Carlo impurity
transport code ERO. A series of methane injection experiments was performed in
the high-density, low-temperature linear plasma generator Pilot-PSI, and
simulated emission intensity profiles were benchmarked against these
experiments. It was confirmed that excitation by D.R. dominates at T_e < 1.5
eV. The results indicate that the fraction of D.R. events that lead to a CH
radical in the A-level and consequent photon emission is at least 10%.
Additionally, quenching of the excited CH radicals by electron impact
de-excitation was included in the modeling. This quenching is shown to be
significant: depending on the electron density, it reduces the effective CH
emission by a factor of 1.4 at n_e=1.3*10^20 m^-3, to 2.8 at n_e=9.3*10^20
m^-3. Its inclusion significantly improved agreement between experiment and
modeling
Density measurements using coherence imaging spectroscopy based on Stark broadening
A coherence imaging camera has been set up at Pilot-PSI. The system is to be used for imaging the plasma density through the Stark effect broadening of the H(γ) line. Local density values are then obtained by the Abel inversion of the measured interferometric fringe contrast. This report will present the instrument setup and proof-of-principle demonstration. The inverted spatial electron density profiles obtained near the cascaded arc source of Pilot-PSI in discharges with axial magnetic field of B=0.4 T are compared with an independent measurement of electron density by Thomson scattering and good agreement is found.This work, supported by the European Communities under
the contract of the Association EURATOM/FOM, was
carried out within the framework of the European Fusion
Programme with financial support from NWO
Dust remobilization in fusion plasmas under steady state conditions
The first combined experimental and theoretical studies of dust
remobilization by plasma forces are reported. The main theoretical aspects of
remobilization in fusion devices under steady state conditions are analyzed. In
particular, the dominant role of adhesive forces is highlighted and generic
remobilization conditions - direct lift-up, sliding, rolling - are formulated.
A novel experimental technique is proposed, based on controlled adhesion of
dust grains on tungsten samples combined with detailed mapping of the dust
deposition profile prior and post plasma exposure. Proof-of-principle
experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are
presented. The versatile environment of the linear device Pilot-PSI allowed for
experiments with different magnetic field topologies and varying plasma
conditions that were complemented with camera observations.Comment: 16 pages, 11 figures, 3 table
Erosion yields of carbon under various plasma conditions in Pilot-PSI
Fine-grain graphite targets have been exposed to ITER divertor relevant
plasmas in Pilot-PSI to address material migration issues in fusion devices.
Optical emission spectroscopy and mass loss measurements have been employed to
quantify gross chemical erosion and net erosion yields, respectively. Effects
of the ion impact energy and target geometry on carbon erosion yields have been
studied. It is concluded that temporal evolution of gross chemical erosion is
strongly connected with changes in morphology of plasma exposed surfaces. The
net carbon erosion yield is increased when the targets are partly covered by
insulating boron-nitride rings.Comment: 14 pages, 4 figures, Contribution to the 19th International
Conference on Plasma Surface Interaction
Molecular modeling of ZnO nanoclusters interacting with various dopant and PVDF
Authors wish to acknowledge the Russian Foundation for Basic Researches (RFBR) grant # 19-01-00519 А
Многокритериальные методы принятия решений в задачах транспортной логистики
The system of methods of multidimensional conditional optimization of ExC is considered and illustrated with an example from transport logistics. The alternative method of decision-making on a set of options on a set of the indicators, uniting possibilities of all ExC models is offered.Рассмотрена и проиллюстрирована примером из транспортной логистики система методов многомерной условной оптимизации ExC. Предложен альтернативный метод принятия решений на множестве вариантов по множеству показателей, объединяющий возможности всех моделей ExC
Ferroelectric nanocomposites based on polymer ferroelectrics and graphene/oxide graphene: Computer modeling and SPFM experiments
The authors are thankful to the Russian Science Foundation (RSF grant # 16-19-10112) and to the Russian Foundation for Basic Researches (RFBR grants # 16-51-53917) for support. Prof. Xiang-Jian Meng expresses his gratitude to the National Natural Science Foundation of China (NNSFC) for support of the project: "The study on the new type of infrared detector based on ferroelectric tunnel junction"
Melt layer motion and droplet ejection under divertor-relevant plasma conditions
Abstract. Accidental melting of metallic plasma-facing materials in future fusion devices poses serious issues regarding the material lifetime and power-handling capabilities as well as core plasma performances. The behaviour of aluminum (as a proxy for beryllium) and tungsten materials has been investigated in the Pilot-PSI linear plasma device to study the melt layer motion and droplet ejection under ITER-relevant plasma conditions
Nanostructuring of molybdenum and tungsten surfaces by low-energy helium ions
The formation of metallic nanostructures by exposure of molybdenum and tungsten surfaces to high fluxes of low energy helium ions is studied as a function of the ion energy, plasma exposure time, and surface temperature. Helium plasma exposure leads to the formation of nanoscopic filaments on the surface of both metals. The size of the helium-induced nanostructure increases with increasing surface temperature while the thickness of the modified layer increases with time. In addition, the growth rate of the nanostructured layer also depends on the surface temperature. The size of the nanostructure appears linked with the size of the near-surface voids induced by the low energy ions. The results presented here thus demonstrate that surface processing by low-energy helium ions provides an efficient route for the formation of porous metallic nanostructures. (C) 2012 American Vacuum Society.</p
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