Browsing by Author "Hildebrandt, D."

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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)
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    Deuterium trapping in divertor tiles of ASDEX-Upgrade
    (Elsevier, 1999) Hildebrandt, D.; Akbi, Mohamed; Juttner, B.; Schneider, W.
    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 contamination
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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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    Quantitative analysis of deuterium in a-C:D layers, a Round Robin experiment
    (2000) Behrisch, R.; Mayer, M.; Jacob, W.; Assmann, W.; Dollinger, G.; Bergmaier, A.; Kreissig, U.; Friedrich, M.; Sun, G.Y.; Hildebrandt, D.; Akbi, Mohamed; Schneider, W.; Schleubner, D.; Knapp, W.; Edelmann, C.
    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 measurements