Premium
Erosion Craters and Arc Cathode Spots in Vacuum
Author(s) -
Jüttner B.
Publication year - 1979
Publication title -
beiträge aus der plasmaphysik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0005-8025
DOI - 10.1002/ctpp.19790190104
Subject(s) - impact crater , cathode , radius , nanosecond , erosion , materials science , current (fluid) , mechanics , optics , geology , chemistry , physics , laser , astrobiology , geomorphology , oceanography , computer security , computer science
The development of erosion craters on clean, smooth cathodes in UHV has been investigated with a time resolution of nanoseconds (current range 10–200 A). Furthermore, crater size erosion rate and velocity of spot displacement have been measured in dependence on current and surface conditions. The relevance of the results for different cathode spot models is discussed in detail. From the measurements the following conclusions are drawn. The craters are caused by the action of the discharge pressure on the molten metal within a spot. The spots move in a random manner in elementary steps of a crater radius with time constants of the order of 10 −8 s. The main reason for the movement is the formation of micropoints at crater boundaries. Droplets and contaminations induce jumps of more than a crater radius. The impact of droplets causes considerable deformations of the cathode surface. Nanosecond pulse breakdowns and quasi‐stationary arcs result in values of crater size, spot velocity and erosion rate that are comparable within an order of magnitude. These results support a non‐stationary spot model that describes the cathode spot as a sequence of surface explosions.