Classification of vacuum arc breakdowns in a pulsed dc system

Abstract

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 α ≈ 1.30, while the secondaries are highly dependent on the pulsing parameters.

In-situ plasma treatment of Cu surfaces for reducing the generation of vacuum arc breakdowns

“…Similar electrodes are described in more detail in Refs. 23,25 . In most measurements, the anode had a smaller diameter than the cathode to minimize the field enhancement near the edges of the electrodes, which is seen in the BDs clustering within a few millimeters from the edge 25 .…”

“…23,25 . In most measurements, the anode had a smaller diameter than the cathode to minimize the field enhancement near the edges of the electrodes, which is seen in the BDs clustering within a few millimeters from the edge 25 . In the experiments performed in Helsinki, the gap length between the electrodes was 40 µm, while for the one pair, measured at CERN, both the anode and the cathode had the same diameter of 40 mm and the gap was 60 µm.…”

“…The electrode types and geometries used in each measurement are listed in Table I. The plasma treatment is performed by inserting the electrodes into a Large Electrode System (LES) vacuum chamber 25 , which was modified to allow gas flow while under vacuum. A schematic of the system is presented in Fig.…”

“…In addition to the LES vacuum chamber, the system includes a power supply, a Marx generator 31 , an oscilloscope and an ion gauge for vacuum pressure measurement. 25,26 . A schematic of the full system can be seen in Fig.…”

Linear voltage recovery after a breakdown in a pulsed dc system

“…These may produce dark current bursts [19,20] that could eventually lead to BDs [21,22]. * anton.saressalo@helsinki.fi According to the statistical behavior of BD events, the latter were suggested to be divided into two major groups: primary (pBD) and secondary (sBD) BD events [23][24][25]. The pBDs were both spatially and temporally independent of the preceding events, whereas the sBDs always follow the pBDs, typically correlating also spatially with the location of the previous BD spot.…”