Spectroscopic investigations in the dense discharge plasma of pseudospark switches

The pseudospark discharge can be subdivided in up to five different phases. In chronological order the first two phases, the low current predischarge and the hollow cathode phase, are well understood. In the following borehole phase the responsible mechanism of electron emission from the cathode material is controversially discussed in the literature. Due to the presented measurements the secondary electron emission caused by impact of discharge gas ions seems to be the favourite candidate. The cathode material seems to be important to start the next discharge phase, the high current phase with the appearance of macroscopic cathode spots. Also higher ionised states of cathode material appear. The last phase in the pseudospark phase, the metal vapour arc, can be compared with typical metal vapour arcs in a vacuum. This arc appears only at very high currents with more than 20 kA and is responsible for the extreme electrode erosion. This strong increase of the erosion at high currents mainly limits the lifetime of the switch. The use of new electrode materials like SiC could reduce this erosion and increase the lifetime. In laser spectroscopic measurements like tomographic two wavelength interferometry a diffuse discharge can be observed with the use of SiC as electrode material, in opposition to a constricted discharge as typical for metal electrodes.