DocumentCode :
1218067
Title :
Evolution of Copper Vapor from the Cathode of a Diffuse Vacuum Arc
Author :
Lins, G.
Volume :
15
Issue :
5
fYear :
1987
Firstpage :
552
Lastpage :
556
Abstract :
The metal-vapor evolution from the cathode of a diffuse vacuum arc is described by a model that starts from the expression for the collisionless expansion into vacuum of atoms originating from an instantaneous point source. The velocity distribution is assumed to be Maxwellian at the moment the atoms are released from the source. By convolution with the vapor generation rate, which is given by an effective erosion rate and the waveform of the arc current, this expression is generalized to yield the atomic density at an arbitrary distance from a point source which emits atoms for a finite period. The result is integrated over the cathode surface which is treated as an extended homogeneous source of vapor. The copper-vapor density was calculated for a vacuum arc driven by a sinusoidal 50-Hz current half-cycle of 500 A rms, for the center of the contact gap. With a vapor temperature of 2000 K and an effective copper-vapor erosion rate of 3 ¿/C, the model well describes the measured decay of the copper-vapor density from about 5 × 1017 m-3 at 300 ¿s before current-zero to 5 × 1014 m-3 at 400 ¿s after current-zero. Comparison with calculations based on the assumption that metal vapor is generated predominantly by molten droplets evaporating in flight indicates that before current-zero the contribution of the droplets to the vapor density is negligibly small, while after current-zero both vapor generation mechanisms produce vapor at the same order of magnitude.
Keywords :
Cathodes; Convolution; Copper; Current measurement; Density measurement; Laser modes; Surface emitting lasers; Surface treatment; Temperature; Vacuum arcs;
fLanguage :
English
Journal_Title :
Plasma Science, IEEE Transactions on
Publisher :
ieee
ISSN :
0093-3813
Type :
jour
DOI :
10.1109/TPS.1987.4316752
Filename :
4316752
Link To Document :
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