Electrical and pyrometric measurements of the decay of the anodetemperature after interruption of high-current vacuum arcs andcomparison with computations

Vacuum arcs of up to 20-kA peak current were investigated. The surface temperature of the anode area melted during the anode spot mode was determined by pyrometry and the evaluation of thermionic currents. The measurements confirm the computations of heating and cooling of the anode, taking into account heat conduction melting/solidification, and evaporation. Pyrometrically obtained temperatures agree well with theory. This gives confidence in the heat conduction model and also shows that the boiling temperature was reached during arcing. Another method evaluates currents of a milliampere value after arcs of several kiloamperes and postarc currents of amperes. Experimental observation (e.g., loading of the shield surrounding the contacts) and theoretical analysis of the interfering effects support the idea that the currents measured are due to thermionic emission     

Motion of high-current vacuum arcs on spiral-type contacts

Motion of vacuum arcs on spiral-type contacts is not only controlled by self-induced magnetic fields, but also by heating phenomena. An expression is derived which permits the calculation of the speed of the arc from a computation of the time needed to heat the surface up to boiling temperature. The heat flux density of the constricted arc at the anode is required as input for the calculation. Good coincidence is achieved with experimental data. The speed of the arc varies from 5 to 400 m/s, depending on experimental conditions     

Laser fluorescence measurements of the flux density of titanium sputtered from an oxygen covered surface

Laser-induced fluorescence spectroscopy is successfully used for the determination of the flux of ion-sputtered wall material. If the surface is clean, the majority of the particles are found in the groundstate multiplet of the neutral atoms. For an oxidized surface, however, excited and ionized states constitute a considerable fraction of the sputtered particle flux. This is investigated in detail in this paper by measuring population densities and velocity distributions of some selected atomic and ionic states of titanium. The respective flux densities and fractions of the total flux density are given, too. A criterion is found which may help to distinguish a clean from a heavily oxidized surface.