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).
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