An Experimental Study of the Photoelectron Work Function Change of Silver-Based Contacts Induced by Arcing in Air

The influence of industrial conditioning (polishing, mechanical shocks and electrical arcs in air) on the electron emission and morphology of contact pastilles made of pure silver [Ag (99.999%)], silver–nickel alloy [Ag–Ni (60/40)], silver–tungsten alloy [Ag–W (50/50)], and silver–tungsten carbide [Ag–WC (50/50)] was investigated. The electronic emission behavior of pure silver Ag and silver-metal alloys (Ag-Me), for both virgin and arced electrical contacts, were studied.Contacts were mounted in a contactor working repeatedly on air (laboratory atmosphere). When submitted to 500 opening electric arcs, the electron work function of an electromechanically conditioned contact Ag-Ni (60/40), measured photoelectrically by using Fowler’s method of isothermal curves, is = (4.50 003) eV at room temperature, while for virgin Ag contacts, it was (4.30 003) eV. The in-crease in the electron work function (EWF) is due to the progressive inclusion of silver oxide in the Ag contact surface during arcing in air.The conditioned (500 arcs) silver-metal alloys studied in this work exhibit the same electronic emission behavior, namely arcing in air increases their EWF. We demonstrated that the electromechanical conditioning by successive electrical arcs affects the surface characteristics such as microstructure, roughness and photoelectron work function

Deuterium and impurity contamination of divertor tiles and collector probes of asdex-upgrade

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

Deuterium trapping in divertor tiles of ASDEX-Upgrade

The deuterium inventory of divertor target tiles used in ASDEX-Upgrade for up to 2000 discharges has been analyzed by thermodesorption spectrometry. In addition, surface analysis techniques as auger electron spectrometry, secondary ion mass spectrometry, nuclear reaction analysis, electron microscopy and optical surface pro®lometry have been applied for investigating erosion and deposition phenomena. The original plasma facing surfaces were graphite (EK98) and plasma sprayed tungsten, respectively. The total deuterium inventories have been found to vary between 4 ´ 1021 D-atoms/m2 and 3 ´ 1023 D-atoms/m2. The deuterium is contained in a deposit on the surface of the graphite and tungsten tiles consisting mainly of carbon, boron and the hydrogen isotopes. There is strong indication that morphological e ects in¯uence impurity deposition, deuterium trapping and re-erosion of the contaminatio

Deuterium trapping in divertor tiles of ASDEX-Upgrade

The deuterium inventory of divertor target tiles used in ASDEX-Upgrade for up to 2000 discharges has been analyzed by thermodesorption spectrometry. In addition, surface analysis techniques as auger electron spectrometry, secondary ion mass spectrometry, nuclear reaction analysis, electron microscopy and optical surface pro®lometry have been applied for investigating erosion and deposition phenomena. The original plasma facing surfaces were graphite (EK98) and plasma sprayed tungsten, respectively. The total deuterium inventories have been found to vary between 4 ´ 1021 D-atoms/m2 and 3 ´ 1023 D-atoms/m2. The deuterium is contained in a deposit on the surface of the graphite and tungsten tiles consisting mainly of carbon, boron and the hydrogen isotopes. There is strong indication that morphological e ects in¯uence impurity deposition, deuterium trapping and re-erosion of the contaminatio

Influence of surface roughness on the deuterium inventoryof ASDEX-UPGRADE divertor tiles

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..

Quantitative Analysis of Deuterium in a-C:D Layers, a Round Robin Experiment

The absolute amount of deuterium in amorphous deuterated carbon (a-C:D) layers has been measured by six laboratories with di erent techniques, such as MeV ion beam analysis, secondary ion mass spectrometry (SIMS), and thermal desorption spectrometry (TDS). The a-C:D layers have been deposited from a CD 4 glow discharge plasma onto carbon and silicon substrates. The results for the absolute numbers obtained with the di erent analysing techniques show a scatter of up to about 35% around the average value. These deviations are larger than the errors stated by the experimentalists and indicate possible systematic uncertainties in some of the measurement

Deuterium trapping in divertor tiles at ASDEX-upgrade

The report discusses surface analysis and thermodesorption as methods for studying the gas content of inner wall components of fusion devices. The following problems are considered: (i) calibration of the thermodesorption, (ii) parasitic adsorption and reaction of released gases at inner walls of the analysing chamber, (iii) gas absorption during storage of the samples in air, (iv) influence of the surface morphology, and (v) influence of deposited layers of carbon and boron. A large number of tiles from the inner and outer divertor of ASDEX-upgrade have been studied. The tiles consisted of pure graphite, massive tungsten, and graphite with sprayed tungsten coatings. Large regions of the inner divertor tiles show thick deposition layers of carbon, boron, and the hydrogenic isotopes containing up to 10"2"3 deuterium atoms/m"2 In the regions of the outer divertor, where erosion processes prevail, the gas content is less by about one order of magnitude, depending in a complicated way on the surface structure and being laterally inhomogeneous. Codeposition trapping is favoured by the surface roughness even in the erosion zones. (orig.)19 refs.Available from TIB Hannover: RA 71(8/15) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman