Communications Internationales

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Author: search.filters.author.Akbi, Mohamed

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    On the temperature dependence of the photoelectric work function of contact materials
    (2014) Akbi, Mohamed
    The nature of the contact material plays a key role to determine the characteristics of the electric arcs and particularly those of the electronic emission. Mechanical and thermodynamic properties as well as electron emission of such complicated alloys present a lack of reliable and accurate experimental data. The purpose of this paper is to present the development of a method for measuring photoelectric work function of pure contact materials that are actually used in relays. Also reported in this manuscript are the results of experimental work whose purpose has been the buildup of a reliable photoelectric system and associated monochromatic ultra-violet radiations source, and the photoelectric measurement of the electron work functions (EWF) of contact materials. In order to study the influence of temperature on the EWF, a vacuum furnace was used for heating the metallic samples up to 700 K. The Fowler’s method of isothermal curves was used for the photoelectric measurement of the EWF. As a first test of the experimental UHV set-up, the EWF of the silver contact materials, namely pure polycrystalline metals (Ag, Cu, Ni, Sn and Zn) were investigated to study the influence of surface cathode temperature on the EWF. In the present study, the photoelectric measurements about silver contacts have shown a linear decrease of the EWF with increasing temperature, i.e. the temperature coefficient dt d􀁉 􀁄 􀀠 is constant and negative: 􀁄 􀀠 􀀐4.58􀂘10􀀐4eV / K in the experiment temperature range [300 K 􀀐 780 K]
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    Influence of surface roughness on the deuterium inventoryof ASDEX-UPGRADE divertor tiles
    (1998) Hildebrandt, D.; Akbi, Mohamed; Jüttner, B.; Schneider, W.
    The gas inventory of divertor target tiles used in ASDEX-UPGRADE has been analyzed by thermodesorption spectrometry (TDS°. desorbed gaseous molecules have been measured by heating up complete and cut divertor tiles. the largest samplrs '80X80mm2)could be heated up to temperatures of 1500 K and smaller ones to even higher temperatures.in addition, surface analysis techniques as auger electron spectroscopy (AES),secondary ion mass spectrometry(SIMS), nuclear reaction analysis (NRA), electron microscopy and optical surface profiling have been applied for investigating erosion and deposition phenomena. the original plasma facing surface of the tiles were graphite (EK98) and plasma sprayed tungsten, respectively. the graphite tiles were used from 1991-1995 for about 1900 discharges and the tungsten tiles in 1996 for about 800 discharges...
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    Deuterium and impurity contamination of divertor tiles and collector probes of asdex-upgrade
    (Fusion and plasma physics, 1998) Hildebrandt, D.; Akbi, Mohamed; Jüttner, B.; Rohde, V.; Schneider, W.
    The uptake and release of hydrogen isotopes at the plasma-facing components in magnetic, confinement fusion devices affects the working gas recycling, the plasma behaviour and the tritium inventory [1]. This attracts considerable interest in the investigation of hydrogen trapping during plasma exposure. The most intensive plasma material interaction occurs on limiters and divertor plates. Post-mortem analysis of such components gives information on the total amount of hydrogen isotopes retained in the material after plasma exposure. Recent investigations of divertor tiles of ASDEX-UPGRADE have shown that the dominant trapped deuterium amount is contained in the deposited material at the surface [2]. This surface contamination consists mainly of carbon, boron and the hydrogenic isotopes. Movable collector probes have been applied to investigate the hydrogen trapping and impurity deposition under specific plasma conditions. In the present paper results on the impurity and deuterium contamination at the surface of collector samples are presented and compared with corresponding results from the divertor tiles. The collector samples were exposed to the scrape-off plasma of the main chamber (SOL-probe) and to the divertor plasma (DIV-probe)