OPTICAL INVESTIGATION OF THE INTERACTION OF A DENSE-PLASMA WITH COLD CATHODES IN AIR

The magnetic blowing of an are against a third so-called commutation e lectrode positioned perpendicularly to the discharge asis allowed a re producible interaction of the plasma with this electrode to be achieve d, Cathodic are spot ignition was viewed on commutation electrodes mad e of Cu, Au, and Ni, High-speed photography revealed that are spot ign ition is initiated either by a luminous layer correlated with a precur rent which is followed by the development of a plasma channel, or by t he formation of a plasma ball, The different structures are attributed to distributions of small sites on the electrode surface which differ in electron emissivity as a consequence of various ion current focusi ng, Scanning electron microscopy shows that the footprint of the chann el or bah is marked with a burning spot with crater marks, The craters differ greatly in shape and size which depend strongly on certain sur face properties.