DocumentCode :
764213
Title :
Why vacuum arc cathode spots can appear larger than they are
Author :
Hantzsche, Erhard ; Jüttner, Burkhard ; Ziegenhagen, Ganka
Author_Institution :
Max-Planck-Inst. fur Plasmaphys., Berlin, Germany
Volume :
23
Issue :
1
fYear :
1995
fDate :
2/1/1995 12:00:00 AM
Firstpage :
55
Lastpage :
64
Abstract :
The visual appearance of arc cathode spots in vacuum is studied experimentally and theoretically. Emission photographs of the spots taken with line radiation have a broad light profile with a rather flat slope (proportional to r with β≈2, r being the distance from the spot center), while photographs taken in absorption are small, having a sharp edge with a steep slope of the profile (β⩾4). Emission photographs from the continuum are similar to absorption photographs. Theoretical analysis shows that the emitted line radiation cannot stem from the locus of excitation. As a consequence, the particles are excited at the edge of the dense spot core, but they radiate at a greater distance due to the finite lifetime of the excited levels and the plasma expansion. Thus, emission photographs from line radiation indicate a greater spot size (about 100 μm) than corresponding to the active spot radius which amounts to ⩽10 μm. This statement holds for discharge durations from 10 ns up to at least 100 μs. The spots exist not only at ignition but during the whole time of the discharge, the location varying due to the spot movement. Absorption photographs show a small size of 10-20 μm still 200 μs after ignition
Keywords :
plasma diagnostics; vacuum arcs; 10 ns to 100 mus; 10 to 100 micron; absorption photographs; broad light profile; dense spot core; emission photographs; emitted line radiation; ignition; line radiation; plasma expansion; vacuum arc cathode spots; visual appearance; Cathodes; Electromagnetic wave absorption; Fault location; Ignition; Optical pumping; Optical surface waves; Plasma density; Plasma materials processing; Plasma sheaths; Vacuum arcs;
fLanguage :
English
Journal_Title :
Plasma Science, IEEE Transactions on
Publisher :
ieee
ISSN :
0093-3813
Type :
jour
DOI :
10.1109/27.376561
Filename :
376561
Link To Document :
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