Showing papers by "William D. Langer published in 1983"

Detection of H/sup 15/NN/sup +/ and HN/sup 15/N/sup +/ in interstellar clouds

Abstract: The nitrogen fifteen isotopes H/sup 15/NN/sup +/ and HN/sup 15/N/sup +/ have been detected for the first time in an interstellar cloud, DR 21 (OH), through obsevations of their J = 1--0 transitions near 90 GHz. These two isotopic species have nearly equal abundances as predicted by ion molecule formation of HN/sup +//sub 2/. Comparison with the weakest component of HN/sup +//sub 2/(F = 1--0) yields an intensity ratio /sup 14/N//sup 15/N>170, consistent with the terrestrial /sup 14/N//sup 15/N isotope ratio (270). The N/sub 2/H/sup +//HCO/sup +/ abundance ratio, which is important for comparison with theoretical chemical models, has been calculated from the H/sup 15/NN/sup +//HC/sup 18/O/sup +/ ratio and, after scaling by the terrestrial nitrogen and oxygen isotope ratios, found to be approx.0.9. This value suggests that in DR 21 (OH) nitrogen could be mostly in the form of N/sub 2/ in the gas phase, while only 10% to 15% of carbon is in the form of gaseous CO. In four other molecular clouds, only upper limits could be established for the H/sup 15/NN/sup +/ and HN/sup 15/N/sup +/ emission.

Axisymmetric scrape-off plasma transport

Abstract: The two-dimensional flow of a collision dominated hydrogen scrape-off plasma in an axisymmetric tokamak is examined. This flow is described by a set of equations which contain the dominant terms in a maximal ordering appropriate to high density experimental divertors and reactor scrape-off plasmas. Comparison of the theory to estimates of scrape-off parameters in the Doublet III expanded boundary plasmas suggests that analysis of classical and neoclassical processes alone may be sufficient to predict plasma transport in high density scrape-off plasmas of practical importance.