  Understanding the microscopic phenomena behind vacuum arc ignition and
generation is crucial for being able to control the breakdown rate, thus
improving the effectiveness of many high-voltage applications where frequent
breakdowns limit the operation. In this work, statistical properties of various
aspects of breakdown, such as the number of pulses between breakdowns,
breakdown locations and crater sizes are studied independently with almost
identical Pulsed DC Systems at the University of Helsinki and in CERN. In
high-gradient experiments, copper electrodes with parallel plate capacitor
geometry, undergo thousands of breakdowns. The results support the
classification of the events into primary and secondary breakdowns, based on
the distance and number of pulses between two breakdowns. Primary events follow
a power law on the log--log scale with the slope $\alpha \approx 1.33$, while
the secondaries are highly dependent on the pulsing parameters.
