Vacuum arc cathode spots as a self-similarity phenomenon
Vakuumbogenkathodenbrennflecken als ein Selbstähnlichkeits-Phänomen
The determination of the basic physical parameters of vacuum arc cathode spots is very difficult due to their small dimensions and short existence times. Values given in the literature for the spot diameter range from less than 10 micrometer up to some hundred micrometers, and spot existence times vary from nanoseconds to some microseconds, caused by the use of different measuring techniques. Using specially designed optical equipment for emission photography, we found structures of cathode spot clusters (short exposure times) and cathode spot traces (long exposure times) which are similar on different spatial scales covering the range from hundreds of micrometers down to 10 micrometer. The light spot traces were found to be similar to scanning electron microscope (SEM) pictures of cathode spot craters, the latter having a higher spatial resolution. The self-similarity over three ranges of magnitude in spatial resolution shows the fractal nature of vacuum arc cathode spot traces.