Investigation of Vacuum Arc Droplets From Copper, Titanium, and Tungsten by Means of Light Scattering

Studies of molten droplets emitted from cathode spots of vacuum arcs on copper, tungsten, and titanium have been carried out using a time-of-flight measurement procedure. In the arrangement, two light barriers at different distances from the cathode surface are used. When particles traverse the barriers, the appearance of scattered light can be used to establish the flight time and, thereby, the velocity of particles. Simultaneously, the intensity of scattered light provides a measure of the size of the particle by applying the Mie-scattering theory together with calibrations. By turning the cathode surface with respect to the drift tube axis, an angular resolution of the parameters was achieved. Algorithms were developed for automated processing of the measured data to identify particles arriving from the arc spot unobstructed. Distributions of the particle sizes, a statistical relation between the sizes and the emission velocities of particles, and other properties are discovered for all three cathode materials.