This special issue is concerned with a better understanding of the
mechanisms in plasmas of the types found in the discharge lamps used for
lighting. Most of these papers originate from presentations made at the
9th International Symposium on the Science and Technology of Light Sources
held at Cornell University on 12--16 August 2001. A small number of papers
from closely related studies have also been included in this special issue.
Arc terminations and particularly cathodes present major challenges for
modellers and experimentalists alike. For the experimenter the difficulties
are that most of the action takes place in very thin layers and that it is
usually only global quantities such as electrode fall and power dissipation
that can be measured without ambiguity. For the modeller, the difficulties
lie in the complex geometries, the poorly known materials constants and,
above all, the wide range of scale lengths involved.
The editors particularly welcome a group of papers from the Ruhr University
in Bochum describing work on arc electrodes that was funded by the German government.
These describe careful measurements of very wide interest on model arcs
in an `ideal' high-pressure argon plasma. The construction of the electrodes
and the experimental technique allow comparisons to be made between various
theoretical models. The result of this extensive work is a very
substantial improvement in the understanding of the termination regions, at
least in argon arcs. Papers from other institutions describe detailed
observations on electrodes in more complicated atmospheres.
Other related papers refer to the modelling of the complete arc with its
terminations, ignition, and the radiation transport within discharges. Many
arcs, both in low and high-pressure discharges, depend on surface layers of
low work function and a number of the papers address this.
The editors hope that bringing this group of papers together will provide a resource
for those aiming for a more complete understanding of the complex behaviour
of discharge lamps.