A study of indexing structures for data in science and engineering

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Studies of mechanisms of hydrogen recycle using a plasma-wall interaction experiment

It is shown that for type 304L stainless steel at room temperature and ion energies of 100 eV a large part of the recycling occurs with hydrogen residence times in the wall of about 100 ms. The use of wall temperatures from 80 to 500 K permits differentiation between thermally activated processes and ion bombardment-induced phenomena. For low energy ions (100 eV) onto 300 K stainless steel walls recycling increases to more than 90% in a few tenths of a second at 3 x 10/sup 16/ ions cm/sup -2/s/sup -1/. For ions up to 300 eV at this flux there is little energy dependence. Both thermally and ion induced processes can be important at room temperature, but under the conditions of this study thermal processes greatly enhance the recycle rates at 300 and 500 K. Preliminary results indicate that recombination of atomic hydrogen to molecular hydrogen can be rate controlling in some practical regimes

Arcing studies in ISX-B

Results of experimental measurements of arcing in ISX-B are described. Samples of stainless steel were exposed at the plasma edge and arcing currents to the sample were measured. Currents from several amperes up to 100 amperes were observed. It was possible to trigger arcs during well-behaved discharges by applying a high voltage to the sample. Elemental analysis of surface features of samples has shown that sulfur segregates to surfaces of arc craters in type 304 stainless steel. Detection of sulfur on surface samples may be related to arcing during cleanup processes in tokamaks

The angular and spectral distribution of transition radiation from thin silver foils

The angular and spectral distributions of photons emitted by Ag foils 660 Å and 1 980 Å in thickness when bombarded by 40 keV electrons have been determined experimentally in the wavelength region from 2 500 A to 5 600 Å. The spectral distribution of light polarized in the plane of incidence showed a sharp peak at 3 300 Å ± 12 Å, this value being an average over photon directions from 10° to 50° from the foil normal. In addition to the peak, the spectrum showed a continuum which decreased slowly with increasing wavelength and a deep minimum at 3 200 Å with a rise in the shorter wavelengths. The angular distribution of photons emitted at the peak wavelength showed a maximum at 30° from the foil normal with zero intensity at 0° and near 90°, whereas the photons emitted at other wavelengths in the continuum, e.g., 2 700 A and 4 500 Å, were most intense at 50° from the foil normal. The absolute photon yield was determined by calibrating the spectrometer, analyzer, and photomultiplier with a tungsten filament lamp obtained from the U. S. National Bureau of Standards. For photon directions from 10° to 40° the photon yield was found to agree with the theoretical predictions in all respects at all wavelengths except at that of the sharp peak where the experimental values were about 30 % lower.On a déterminé expérimentalement les distributions angulaire et spectrale, dans le domaine de longueurs d'onde de 2 500 Å à 5 600 Å, de photons émis par des feuilles d'argent de 660 Å et 1 980 A d'épaisseur lorsqu'on les bombarde avec des électrons de 40 keV. La distribution spectrale de la lumière polarisée dans le plan d'incidence a montré un maximum aigu à 3 300 Å ± 12 Å. Cette valeur est une moyenne évaluée sur 1'ensemble des directions faisant avec la normale à la feuille des angles allant de 10° à 50°. En plus de ce maximum, le spectre présentait un fond continu dont l'intensité décroissait lentement lorsque la longueur d'onde augmentait,et un faible minimum à 3 200 A, suivi, pour les longueurs d'onde plus courtes, d'une augmentation d'intensité. La distribution angulaire des photons émis, pour la longueur d'onde correspondant au maximum, présente un maximum à 30° de la normale à la feuille. Aucun photon n'est émis perpendiculairement ou tangentiellement à la feuille. En revanche, la lumière émise pour d'autres longueurs d'onde du fond continu, par exemple 2 700 Å et 4 500 A, était surtout intense à 50° de la normale. On a déterminé le rendement lumineux absolu après avoir étalonné le spectromètre, l'analyseur et Ie photomultiplicateur avec une lampe à filament de tungstène provenant du U. S. National Bureau of Standards. En ce qui concerne les directions faisant un angle de 10°. à 40° avec la normale, le rendement lumineux était en tout point en accord avec les prévisions théoriques pour toutes les longueurs d'onde sauf pour celle correspondant au maximum aigu pour laquelle la valeur expérimentale est inférieure de 30 % environ