Vacuum Arc Discharge
Vacuum arcs, also referred to as cathodic arcs, are high current discharges between cold electrodes. Typical currents are 100 Amperes or more while the voltage between anode and cathode is only about 20 Volts.
The current at the cathode is concentrated in small, mobile "hot spots". Fully ionized metal plasma is produced at these cathode spots. However, not only metal plasma but also tiny droplets of diameter 0.1 - 10 µm are produced. They are usually called "macroparticles" to emphasise their massive nature compared to plasma particles (ions, electrons, atoms). For some applications, for instance the deposition of thin films with optical quality, macroparticles are not acceptable, devices for plasma and macroparticle separation are used (macroparticle filters).
One of our contributions to the field of vacuum arc plasma physics was the investigation of ion charge states. The ion charge state distributions (CSD) of 50 metallic elements have been measured (see I.G. Brown, Review Scientific Instruments, vol. 65 (1994) 3061-3081...). Charge state distributions are the result of ion formation at hot cathode spots and "freezing" in the expanding plasma (see A. Anders,Physical Review E, vol. 55 (1997) 969-981).