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Numerical and experimental investigation of thermal regimes of thermionic cathodes of arc plasma torches
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Abstract(s)
The modelling method based on decoupling the simulation of the cathodic part of the arc (the
cathode and the near-cathode non-equilibrium plasma layer) from the simulation of the arc on
the whole has been extended to cathodes of arc plasma torches, consisting of an insert with a
conical tip, made of pure or doped tungsten, and a surrounding water-cooled copper holder. The
method was validated by comparison with the experiment, performed on a 200 A DC arc in
atmospheric-pressure argon. Standard work function of polycrystalline tungsten of 4.54 eV was
used for modelling of pure-tungsten insert and a good agreement with the experiment was found
with respect to both the insert tip shape and the temperature distribution in the tip, recorded in
the stable operation mode. There are no unambiguous data on the work function for arc
cathodes made of doped tungsten, although in situ measurements of the effective work function
of cathodes of high-pressure arc discharges provide useful hints. On the other hand, the
experiments reported in this work show that the tip temperatures of inserts made of tungsten
doped with 1.5% of thorium, or lanthanum, or yttrium, recorded during the stable-mode
operation at the arc current of 200 A, vary in a rather narrow range 3100–3200 K. This suggests
that the work functions of doped tungsten inserts, operated in the stable mode, are close to each
other as well. Indeed, the results of modelling with the same value of the work function of 3 eV
give a reasonably good agreement with the experiment in all three cases.
Description
Keywords
Numerical Experimental Investigation Thermionic cathodes High-pressure arc discharges Deviations from local thermodynamic equilibrium . Faculdade de Ciências Exatas e da Engenharia
Citation
Publisher
IOP Publishing