Plasma cleaning of ITER first mirrors in magnetic field

To avoid reflectivity losses in ITER optical diagnostic systems, plasma sputtering of metallic First Mirrors is foreseen in order to remove deposits coming from the main wall (mainly beryllium and tungsten). Therefore plasma cleaning has to work on large mirrors (up to a size of 200*300 mm) and under the influence of strong magnetic fields (several Tesla). This work presents the results of plasma cleaning of aluminium and aluminium oxide (used as beryllium proxy) deposited on molybdenum mirrors. Using radio frequency (13.56 MHz) argon plasma, the removal of a 260 nm mixed aluminium/aluminium oxide film deposited by magnetron sputtering on a mirror (98 mm diameter) was demonstrated. 50 nm of pure aluminium oxide were removed from test mirrors (25 mm diameter) in a magnetic field of 0.35 T for various angles between the field lines and the mirrors surfaces. The cleaning efficiency was evaluated by performing reflectivity measurements, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy.Comment: 5 pages, 6 figures and 1 table. Results presented on the 21st Plasma Surface Interaction conference held in Kanazawa Japan, May 201

Decomposition studies of NH₃ and ND₃ in presence of H₂ and D₂ with Pt/Al₂O₃ and Ru/Al₂O₃ catalysts

In the fusion reactor ITER, ammonia will be produced as a result of the interaction between the hydrogen isotopes used as fuel and nitrogen used to spread the power loads of a larger area. As part of the fuel management in ITER, NQ3 (NQ3, Q = H, D, T) will have to be decomposed using a palladium membrane reactor. The decomposition of pure NH3 and ND3 was studied in this work using commercial platinum (Pt) and ruthenium (Ru) catalysts on alumina (0.5 wt% loading), in a conventional reactor configuration (i.e., without a palladium membrane). With Pt/Al2O3, decomposition fractions larger than 90% were achieved with NH3 above 800 K using the lowest flow-to-mass ratio (/g-cat) of 0.015 sccm g−1. However, with the increase of /g-cat to 0.220 sccm g−1, similar decompositions were achieved only at  K. In contrast, with Ru/Al2O3 decomposition fractions above 90% were attained already below 700 K, regardless of /g-cat. With both catalysts the decomposition of NH3 was found to be more efficient than that of ND3 at a wide range of temperatures, thus evidencing the existence of isotopic effect. A strong inhibition of both NH3 and ND3 in presence of, respectively, H2 and D2 with Pt/Al2O3 was observed. This effect was stronger at lower temperatures and larger hydrogen partial pressures. The inhibition effect with Ru/Al2O3 was less pronounced and it was suppressed at 629 K. Isotopic exchange reactions with equimolar mixtures of NH3-D2 and ND3-H2 revealed that the most and least abundant isotopologue are, respectively, NH2D and ND3. At the relevant temperature window in which the PMR will be operated (673–823 K), the Ru-based catalyst exhibits superior performances in terms of decomposition rates, negligible isotopic and inhibition effects. A slight reduction of the performances with this catalyst was observed with 0.200 sccm g−1. This work suggests that 0.5 wt% Ru/Al2O3 is the most suitable catalyst to be used during ITER operation

Kurzeinführung Literaturrecherche Wiwi

Folien für die Veranstaltung "Einführung in die Literaturrecherche für Wirtschaftswissenschaftler an der TU Darmstadt

Electronic Publishing in academic contexts: quality control and usage scenarios

Ziel der Arbeit ist die Entwicklung eines qualitätsorientierten Beschreibungsmodells für Nutzungsszenarien in E-Publishing und E-Learning. Wichtige Trends wie die Transparenz und Offenheit von Formaten, Strukturen und Prozessen werden einbezogen (Open...-Bewegung), ebenso die Frage nach kollaborativen Ansätzen in der Wissenschafts- und Bildungskommunikation (Web 2.0 und Community-basierte Ansätze). Zentral ist dabei neben der qualitätsorientierten Herangehensweise vor allem die Erarbeitung eines integrierten Ansatzes für deren Unterstützung und qualitätsorientierte Entwicklung und die Identifikation verschiedenener Nutzungsszenarien. Zunächst wird ein detaillierter Blick auf das elektronische Publizieren und Lernen im wissenschaftlichen – vorwiegend universitären – Umfeld geworfen. Der Markt der Bildungsökonomie wird untersucht, Produktion, Distribution, Evaluation und Nutzung werden kritisch beleuchtet. Nach einer aktuellen Darstellung des Qualitätsbegriffs folgt die Entwicklung eines umfassenden und konsistenten Modells zur qualitätsorientierten Beschreibung und Bewertung von internetbasierten Publishing- und Learning-Services und -Produkten. Dieses wird dann angewandt auf diverse Nutzungsszenarien wie z.B. Blended Learning, Print-on-Demand, Collaborative Publishing, Digitalisierungsprojekte oder Sicherstellung der Langzeitverfügbarkeit. Dabei bettet die Arbeit das Thema breit in einen Rahmen aus Informationswirtschaft, Informatik, E-Business, Wissensmanagement, E-Learning, Wirtschaft und Qualitätsmanagement ein. Zentrales Ergebnis ist ein sehr breit anwendbares Beschreibungs- und Bewertungsmodell für digitale Content-Angebote und -Dienstleistungen. Ein abschließendes Kapitel entwickelt eine Typologie der Geschäftsmodelle einschlägiger Service-Anbieter und wirft einen Blick auf zukunfts- und konfliktträchtige Themen wie eScience und Grid, Plagiate oder mandatorische Open Access-Policies.The work's main purpose is the development of a quality-centered description model for usage scenarios in E-publishing and E-Learning. Important trends like transparency and openness of formats, structures and processes are integrated (Open...-Movement) as well as aspects of collaborative attempts in scientific and educational communication (Web 2.0 and community-based scenarios). Beside the quality-oriented approach, the central idea is the development of an integrated model for description and evaluation of digital content products and services, for their support and development, and the identification of different usage scenarios. At first a detailed look is directed at electronic publishing and learning in the scientific - mainly academic - sphere. The market and economic circumstances of higher education are examined, production, distribution, evaluation and reception are critically analyzed. A topical representation of the concepts of quality is followed by the development of a comprehensive and consistent model for quality-oriented description and assessment of internet-based publishing and learning services and products. This model then is applied to various usage scenarios such as blended learning, print-on-demand, collaborative publishing, digitization projects or long term preservation. The subject is examined on a broad basis, covering e-business, information business, knowledge management, e-learning and quality management, information technology and computer science. Central result is a very broadly applicable description and assessment model for digital content products, services and service providers. A final chapter draws a typology system of appropriate business models and looks at promising or controversial subjects like eScience and Grid, plagiarism or mandatory Open Access policies

Ion flux-energy distributions across grounded grids in an RF plasma source with DC-grounded electrodes

We present an experimental investigation of the ion flux–energy distribution functions (IFEDFs) obtained across grounded grids in an asymmetric capacitively coupled RF source using a helium discharge. The powered electrode in the RF source is DC-grounded via a λ/4 filter, which lifts its DC potential to zero. Grids of different dimensions (hole width, thickness, and geometric transparency) were used to confine the plasma, while the IFEDF of the ion beam departing the grid and reaching the reactor walls was studied using a retarding field energy analyser. The IFEDF obtained was double-peaked, indicating the presence of fast ions arriving from the plasma source, and cold ions generated upon charge exchange collisions between the fast ions and neutrals. The flux, as well as the peak energies of the two ion groups, depended significantly on the process parameters: RF power, He pressure, the distance between grids and walls, and the dimensions of the grids. The results indicate that confining plasma with grids can reduce the ion flux at the walls by over 60%, significantly lowering the wall sputtering rate. This was confirmed with a dedicated long-exposure plasma discharge with a gridded plasma reactor, wherein less than 1 nm of Cu deposition was found on the DC-grounded powered electrode, and the surface reflectivity was preserved to pristine values. In contrast, a similar experiment in a gridless reactor resulted in Cu deposition of 35 nm with a drastic drop in surface reflectivity. These studies are of great importance for the application of similar RF plasma sources with in-situ cleaning of diagnostic mirrors in fusion devices, as well as in a variety of plasma processing applications

Atomic Friction Investigations on Ordered Superstructures

We review recent friction measurements on ordered superstructures performed by atomic force microscopy. In particular, we consider ultrathin KBr films on NaCl(001) and Cu(001) surfaces, single and bilayer graphene on SiC(0001), and the herringbone reconstruction of Au(111). Atomically resolved friction images of these systems show periodic features spanning across several unit cells. Although the physical mechanisms responsible for the formation of these superstructures are quite different, the experimental results can be interpreted within the same phenomenological framework. A comparison between experiments and modeling shows that, in the cases of KBr films on NaCl(001) and of graphene films, the tip-surface interaction is well described by a potential with the periodicity of the substrate which is modulated or, respectively, superimposed with a potential with the symmetry of the superstructur